Diesel engines are not as popular in superminis as they are in larger cars, and that might partly explain Suzuki's apparent tentativeness on the subject. The first diesel Swift became available in the UK as recently as last June, some time after the rest of the revised range went on sale, and even now there is only one version.It's a five-door, it has manual transmission only (no automatic, though such a thing is offered as an option on petrol Swifts) and it's in the mid-range SZ3 trim level. Standard equipment therefore includes 16" alloy wheels, air-conditioning, a USB port, heated door mirrors and, following Suzuki's award-winning safety policy, no fewer than seven airbags.For various reasons, diesel engines are costly things to build, and while this car is not the most expensive Swift you can buy, it is the most expensive SZ3 by £1200. This is something of a problem, because despite having a good deal of charm the Swift doesn't feel much like a premium product even in petrol form, and the diesel is unpremiumer still.Mostly, that's because it makes a frightful racket. From a cold start it sounds as if someone has put a toolbox in a tumble dryer, and even when warm there are more gurgles and rattles than a gentleman might wish for.If you can live with that, there are compensations. The maximum power output is 74bhp and 0-62mph takes more than 12 seconds, but if you had asked me at any point during this test (which was a long one - three weeks and well over 2000 miles) I would have said that both figures were better than that. The car generally feels quicker, and in fact it picks up so rapidly - once the turbo has got up to speed - from 1700rpm or so that you have to be careful with your right foot to prevent it jumping forward too enthusiastically in town.According to the official EU test, the Swift diesel has combined fuel consumption of 67.3mpg and CO2 emissions of 109g/km. These are the best figures of any Swift, though as far as Vehicle Excise Duty is concerned the second one means simply that you have to pay the Chancellor £20 per year rather than the £30 you'd be charged if you bought a 1.2-litre petrol model instead.As for the consumption figure - well, you know what they're like. A colleague was rightly lauded last year for achieving 86.4mpg in an identical car, but that was during an economy marathon when competitive spirits were high. On this test - according to the trip computer, whose accuracy was supported to the nearest tenth by measurement - the Swift went through diesel at the rate of about 56mpg almost regardless of what I was doing with it, though it did reach 60mpg during a rare two-hour spell of good weather on a long motorway trip.This isn't bad, but there are larger and more powerful diesel cars which can do as well, or in some cases quite a lot better. And, bearing in mind the extra cost and noise, I think there would have to be a much more spectacular improvement in fuel economy over the 1.2 petrol (which you can read about in this review) for the diesel version to make sense. Engine 1248cc, 4 cylinders Power 74bhp Transmission 5-speed manual Fuel/CO2 67.3mpg / 109g/km Acceleration 0-62mph: 12.7 seconds Top speed 103mph Price £13,355 Details correct at publication date