Referring to what he called "the action of Russia", Sir Winston Churchill said: "It is a riddle, wrapped in a mystery, inside an enigma." Years later, the same terminology could be applied to the anomalies of the diesel engine, misunderstood by many. Are they really high polluters? Why do they have a common rail - is it something to do with railway engines? Do you still have to change the oil much more often and wait for the glow plugs to warm up?    The answer to all these questions is that the diesel engine has made enormous strides in recent years, the biggest improvement being the development by Audi of direct fuel injection into the cylinders. Diesels used to be very harsh if fuel was injected this way, so manufacturers used a small pre-combustion chamber in which the firing stroke started. A few still do it this way, but most are now direct and the Audi engine principle of two-stage injection is applied also to Volkswagen, SEAT, and koda.
   With direct injection comes much shorter delay before cold start-up is possible. They still have glowplugs to warm the combustion area, but with the modern diesel you never have to wait more than two or three seconds for this and then only in very cold weather. Indeed, the reliable starting of the diesel is one of its joys, especially on a cold, damp morning when petrol engines may be suffering from damp electrics.
   For improved efficiency, manufacturers have found it best to supply the fuel under enormous pressure to all cylinders and arrange for the injection to be metered accurately into the engine, instead of the previous arrangement of sending a pulse to each cylinder in turn. As a result, the supply is from a single pipe or gallery - hence the stupid name 'common rail'. Citroân and Peugeot call it HDI (high pressure direct injection).
   Exhaust emissions have been reduced and will come down further with introduction of what is called a 'particle trap'. It will trap particles which give the smokey look to diesel exhaust and burn them off. Ford led the way in extending oil change intervals and most diesels now go at least 5,000 miles between oil changes.
   So, it's all looking good for diesel cars and, as you'll gather from these tests of six top contenders at various price levels of the market, they're now very acceptable to drive as well as being even more economical.
   Prices are as listed at the beginning of October. Fuel consumption figures are those actually measured for Wessex Wheels and not those quoted by manufacturers. Acceleration time from rest to 80 mph is given for each car as this gives a more significant comparison of performance than the more familiar 0 to 60 mph. Neither this nor the maximum speed figures imply that these speeds should be attained where lower limits apply.

Ford Focus Zetec 1.8TDdi 5-door
Driving Ford's new Focus is always a pleasure and I rated this diesel version the best Ford diesel I have yet tried. Their 1.8-litre turbo unit has tended to be a bit harsh, but there was nothing of the kind to criticise in this latest example, which proved very prompt to start, extremely smooth and quiet, with vigorous torque and acceleration. It's a direct injection diesel with intercooler and throttle control is electronic - meaning that there is no cable or rod control - it's all done by wires. You don't like the idea of that? Then never again fly in an aircraft, because that's how most of their engines are controlled!
   Fast cruising is effortless and relaxed and there is not a lot of need for frequent gear changing, in spite of the high gearing. The gear change itself is very easy to use, with a large gear knob and light clutch action.
   The suspension gives a comfortable ride, with not much tyre roar or thump and good bump absorption. The brakes respond well to light pedal loads, but it's perhaps surprising that Ford don't put in anti-lock control as standard. It can be added, as part of a 'Reflex' package costing £500, which includes rear disc brakes instead of drums, plus traction control and side impact front airbags.
   This package was not on the test car, but it did have the optional 'climate' pack (also £500) bringing air conditioning, plus electric heating for the windscreen, mirrors and washer jets. It also had the optional (£250) winding handle glass sunroof - hooray! I'm afraid I'm one of the funny minority of British drivers who would rather have a sunroof than air conditioning, but to have both is ideal. I enjoy the extra light coming in through the glass even when it's closed, but I am not keen on the electrically heated windscreen, because I am aware of the wire matrix, especially when seen against the sky.
   Seats are well-shaped, with winding handle height adjustment for the driver and give good support in the small of the back. A large rotary knob adjusts the backrest angle. The rear seat is divided 60/40 and can be folded down on to the cushion, or the cushion can be tipped forward first but it is in one piece.
   The Focus turbo diesel is available as four-door saloon, five-door hatchback (as tested), or estate. Ford always favour a self-locking tailgate, but it can be opened readily either by the conveniently placed button to the right of the facia panel, or by pressing (for at least a second) the button on the remote locking sender. It's a generously roomy load compartment. A key-operated lock concealed behind the Ford badge opens the bonnet.
   Highest praise is deserved for the stylish yet functional facia layout and for the audio unit with large, clearly legible controls. In standard form it plays cassettes, but the one on the test car had been upgraded to the 6000, which plays CDs. A nasty economy is the lack of any map reading light.
   Both in overall concept and in most of the small detail matters, Focus attracts.

Ford Focus Zetec 1.8TDdi - £14,000
Petrol version cheaper? Yes, 1.8 saves £500
Warranty - 1 year unlimited mileage
              - 6 years anti-corrosion
Maximum speed - 125 mph
0-80 mph - 23.6 sec
Fuel consumption - 51.0 mpg
Insurance - Group 5

SEAT Toledo SE 1.9 TDi
It shows the popularity of the VAG turbo diesel engine that it appears in half of the cars selected for this group - the Audi A3, Volkswagen Bora and here, the SEAT Toledo. It's the same in each case and equally impressive in them all. Trying it in the Toledo, I noted that it could almost be a petrol engine for its quietness and excellent throttle response.
   One thing common to all these diesel engines is very high overall gearing, which means that when cruising fast there's just a subdued rhythmic beat from the engine which, in the Toledo, won't have reached even 3,000 rpm until well over 80 mph. Usually this also means that a lot of gear changing is necessary on ordinary roads. Well, you certainly use the gearbox rather more even with this tractable diesel engine, but the low-speed torque is so good that it will trickle along with the 30 mph traffic stream in fourth and pick up very well in third.
   The suspension in the Toledo gives an odd mixture of ride characteristics - good for its absorption of small bumps and for the low level of tyre roar, but inclined to be a bit loose and buckety over big undulations. The steering is precise, with light weight and good lock and the wheel is attractive with its thick rim in stitched leather and large circular boss. It adjusts both ways - vertically and telescopically.
   Anti-lock brakes are standard, with discs front and rear, and response to the pedal is reassuring, hauling the speed down very well when needed.
   Although the seats are comfortable with ample lumbar support and soft upholstery, they look rather drab even with the car nearly new. A ratchet lever at the side gives height adjustment. A centre armrest in the front compartment serves also a small storage compartment in which a mobile 'phone might be left out of sight. In the rear compartment, the seats and their cushions are divided 40/60, with easy folding provision to extend the load compartment. However, the boot space is really enormous. A full-size spare is in the well below the boot floor, but it is mounted on a steel wheel, while the fitted wheels are alloys.
   In the modern trend, the Toledo gets air conditioning with digital display, but no sunroof. It's available as an option at £585, as is leather upholstery for a modest £295. Alternatively, the buyer can specify leather with electric seat adjustment and memory so that chosen positions are regained at a touch, for £1,395. Generous standard equipment includes a trip computer, but on the test car it had an odd fault: 24.2 mpg, it indicated! I knew that was wrong, as proved when the car returned near 50 mpg. There must have been a fault in its calibration. This is part of the SE package, which also brings a CD auto-changer, front centre armrest, climate control for the air conditioning, cruise control and side airbags.
   Toledo is strictly a four-door saloon and one that is bound to please, offering sound value and low running costs. If you prefer a five-door hatchback, then there is not long to wait, as the Le¢n - which is effectively a Toledo five-door - was launched at the recent Frankfurt Show, to go on sale here early next year.

SEAT Toledo SE 1.9 TDi - £16,895
Petrol version cheaper? Yes, £900
Warranty - 3-year unlimited mileage (dealer)
              - 12 years anti-corrosion
Maximum speed - 120 mph
0-80 mph - 20.8 sec
Fuel consumption - 49.6 mpg
Insurance - Group 9

Citroân Xantia 2.0 HDI LX Estate
Using their own models as the yardsticks, Citroân demonstrate how the new HDI (High pressure direct injection) diesel engine in the Xantia saves money. The fuel consumption on the official figures for the Xantia hatchback averages 51.4 mpg. With the former 2.1-litre turbo diesel engine, before HDI came on the scene, it was 40.4 mpg and with the 1.8-litre 16-valve petrol engine it is 32.5 mpg. Even before future threatened fuel price increases, the saving compared with the petrol engine is more than £2,000 in 60,000 miles.
   But it's not only the fuel saving that is so remarkable with the new HDI engine: it's also the effortless way in which it performs, with vigorous low-speed torque, impressive smoothness and noise levels not much higher than those of the far more expensive BMW.    All the driving controls are precise including very accurate steering and effective all-disc brakes with anti-lock control, although with an unexpectedly hard feeling to initial pressure on the brake pedal. The Xantia takes corners reassuringly and with little body roll - an advantage of its special suspension.
   The car for this test was an Estate, with its roomy load compartment, easy-to-lift tail door and low floor without any obstructive rear sill. As well as providing an extremely comfortable ride, the Hydopneumatic suspension - unique to Citroân - allows the static height to be lowered, making it much easier to slide heavy items in or to pack them on the roof. Longitudinal roof rack runners are provided for easy fitting of an optional roof rack.
   Seats are in soft velour-type fabric which locates well and the driver has adjustable lumbar support as well as a pull-out lever on the right for height adjustment. The rear seats are divided 40/60 and the seat folding arrangement is ingenious: the cushion is pulled forward first, then tipped and the backrest drops down into the space available making a level extension of the load platform. The removable rear shelf has a pull-out roller blind beneath to cover the back part of the load space when required.
   A pleasant surprise with this Xantia came when driving it on a motorway for the first time, when the Trafficmaster system suddenly warned of a delay problem ahead. This is a standard feature of all Xantias from LX upwards.
   Generous standard equipment also includes twin front airbags, electric adjustment for the mirror on the passenger side, a map reading light above each front door and air conditioning. Sunroof with electric action is available, but costs £410 extra. The radio/cassette is easy to operate, with a clear display panel, and there are repeater controls on the steering wheel. Another digital display shows time, outside temperature, and date.
   A very pleasing and spacious load carrier, the Xantia Estate with the advantage of its HDI diesel engine is a very strong contender, but the extra cost for this new engine is high.

Citroân Xantia 2.0 HDI LX Estate - £18,430
Petrol version cheaper? Yes, 1.8LX £2,745
Warranty - 1 year unlimited mileage
(extendable to 2/3 years)
               - 6 years anti-corrosion
Maximum speed - 116 mph
0-80 mph - 20.9 sec
Fuel consumption - 47.2 mpg
Insurance - Group 11

Volkswagen Bora Sport TDI
In these days when manufacturers no longer display the model designation on the boot lid, it's not always easy to know exactly what car has been provided for test. When examining the Bora for the first time, I wondered what it was. SE, perhaps? No, it turned out to be the Sport version. Why Sport, I queried, thinking that it would have harder suspension not to mention dearer insurance. But when I examined the specification, I found that it comes with some very comfortable and attractive front seats, a very appealing three-spoke leather trimmed steering wheel, front fog lamps incorporated in the headlamps, smart Le Castellet alloy wheels and walnut wood inserts on the console and doors.
   The more I lived with this car, the more I wanted to have one and it's definitely on my short list for purchase when (or is it if?) prices get more reasonable. The engine is excellently quiet and smooth and seemed to give more than 50 mpg on a run. In many respects, of course, it's very similar to the SEAT Toledo which we also test here, but careful comparison showed it to be better in many respects, notably the ride comfort, as well as looking more attractive inside. This is much as to be expected, since it costs quite a lot more in the Sport specification.
   There are also many attractive details which add to its appeal and, while some may be available on other models near the Bora's price, not all of them are to be found elsewhere. Such little matters as provision of a concealed switch to turn off the alarm sensors when a dog is to be left in the car, the way in which the door lock buttons disappear when the doors are locked, the secret electric boot release and the two-stage trip computer which resets one of its stages when the car has been parked for several hours. All too often I set off for a journey and am well under way when I realise that I didn't set the trip recorder - but the Bora will have done this automatically.
   Other things to be liked are the way in which the wipers park out of sight at the bottom of the windscreen, the red warning lights that come on when a door is open, and the excellent radio/cassette unit with digital display of chosen station between the speedometer and rev counter.
   Do you ever find it irritating to have to keep turning the wipers on to clear spray thrown up by another vehicle? Not necessary on the Bora: automatic wiper action and self-dimming of the interior mirror are standard features of SE models and above.
   The only thing I wouldn't go for, I'm afraid, is the navigation system. It would get you there in the end, but only after taking the most extraordinarily round-about route. The Bora Sport TDi is quite expensive enough without paying another £2,500 for the marvel of an on-board navigator.

Volkswagen Bora Sport TDI - £18,630
Petrol version cheaper? Yes, 2.0 £1,120
Warranty - 3-year unlimited mileage
              - 12 years anti-corrosion
Maximum speed - 120 mph
0-80 mph - 20.0 sec
Fuel consumption - 47.3 mpg
Insurance - Group 8E

Audi A3 1.9 SE TDI 110
When the A3 first appeared in the summer of 1996, it was Audi's first car with a transverse engine. Only petrol engines were offered at first, but the more powerful of the two 1.9-litre turbo diesels followed in 1997. In this form, the A3 is a very pleasing car indeed, offering lively performance, a very quiet and refined power unit and fuel economy consistently above 50 mpg.
   As tried, the A3 had the Special Equipment package, in which the main feature is air conditioning with digital climate control. The A3 SE also comes with alloy wheels, Alcantara upholstery, front armrest and automatically dipping rear mirror, which doesn't add up to enough to justify a £2,310 increase in the price. This takes the total to £19,361, making the A3 look very expensive indeed.
   The pay-off is that it is delightful to drive, very comfortable and extremely well built and furnished - though some may find the all-black or dark grey interior a little sombre. The A3 will appeal to those who want a luxury - perhaps in a car for retirement - but don't want a big car, and for whom price is not a major consideration.
   As well as having an excellent engine, the A3 is very easy and reassuring to drive, with firm but not harsh suspension, precise steering and gear change and exceptionally keen all-disc brakes which respond to the lightest touch on the pedal.
   A five-door A3 was added to the range in January this year. The three-door, as tested, has the advantage of very easy single-handed action to tip either front seat bodily forward for unobstructed access to the rear seat, which is wide enough for three to sit abreast. The rear seat is divided 40/60 with provision for either or both parts to fold down on to the cushion, or the cushion is also divided and can be tipped forward first for a level extension of the load platform. Luggage space is generous in relation to the compact size of the A3 and the tailgate is light to lift.
   Generous features are the on-board computer, giving a satisfying mpg reading often above 55, the impressively clear instruments, electric heating for the seats and the provision of two map reading lights and twin airbags. But such a car should have a sunroof, especially as there is no air conditioning on the standard model. Sunroof is an option at £801.
   Not typical, I'm sure, was a strange fault on the test car: both door mirrors were loose in their surrounds and wrongly made, so that they could not be pushed back in. One actually came adrift, but didn't fall and break - it hung from the wire for the electric heating. Otherwise everything about the A3 adds up to a most pleasing modern diesel car. It's expensive, but not as bad as it used to be: Audi reduced the price this summer by £1,176, from £20,537 to £19,361.

Audi A3 SE TDI 110 - £19,361
Petrol version cheaper? Yes, 1.8 saves £139
Warranty - 3 year unlimited mileage (dealer)
              - 12 years anti-corrosion
Maximum speed - 121 mph
0-80 mph - 19.8 sec
Fuel consumption - 52.5 mpg
Insurance - Group 12

BMW 530d SE automatic
Wow! When I looked at the price list for the BMW I had been testing and then added on the price of the toys with which it was equipped, I was looking at a total of nearly forty grand! So who, you might ask, is going to be worried enough about the cost of fuel to specify the diesel version of such an expensive car? Well, the explanation is that not everyone will run to such an extravagant list of equipment - BMW obviously wanted to show what is available - and it's not only for the fuel economy that people go diesel. What is also very attractive is the ability to cover great mileages without the delay of stopping for fuel. Also, many executives bear in mind the cost of fuel on long Continental journeys when they may be on holiday and having to fork out for it out of their own pockets.
   On the credit side, too, is that the six-cylinder direct injection turbo diesel in the BMW 5-Series is undoubtedly one of the best available offering smooth, effortless performance, exceptionally quiet long-legged cruising, and a satisfyingly purposeful growl when the driver puts the foot down.
   You can have the 530d SE, as this BMW is called, with six-speed manual gearbox or, for £1,220 extra, five-speed automatic with Steptronic control. BMW automatics used to be horrid, but I really took to this one, with its excellent control system. To move off, the driver pulls the selector back from P position to D, remembering that it won't come out of P or N without the driver's foot on the brake pedal - a precaution to stop American drivers from getting muddled up and driving through the garage wall! From then on, it's all automatic and very responsive, but if an over-riding down change is needed, perhaps for engine braking ready for a corner, all that is needed is to knock the lever to the left. Then, pushing it forward or backwards changes up or down, one gear at a time. Simple, and very effective - I liked it.
   There's much more to like in the BMW, of course, notably the very comfortable ride, the decisive handling, helped by having rear-wheel drive to give better balance, and the wonderfully responsive brakes. The steering is a shade on the heavy side, but has a positive feel and is accurate at speed. The column is adjustable both telescopically and vertically. The wheel has cruise controls on the left and audio controls on the right.
   Among the luxuries added to this 530d SE were leather upholstery for the sumptuously shaped seats, adding £1,580 to the bill. It also had (at £3,795) BMW's elaborate and very impressive navigation system which comes complete with television. You thought television wasn't allowed in the front of a car? Well, it isn't, so it stops as soon as you start the engine. The navigation system presents a wonderfully clear map, whose display can be changed from 125 yards progressively to 50 miles, but sadly it makes some very odd choices of route.
   This is diesel motoring par excellence and it's the sort of car I would choose to convince anyone that a modern diesel car can be fast, quiet and smooth.

BMW 530d SE automatic - £30,615
Petrol version cheaper? No, 528i SE £1,700 dearer
Warranty - 3 years 60,000 miles (dealer)
              - 6 years anti-corrosion
Maximum speed - 138 mph
0-80 mph - 13.9 sec
Fuel consumption - 39.3 mpg
Insurance - Group 15