A couple of weeks ago I drove the Cooper S version of the MINI Roadster. As you can see from this review, I didn't like it much. My main objection was that it seemed to have too much power for a body structure that has lost a lot of stiffness in the process of having the roof removed from the Coupé on which it's based.If you buy a Cooper SD instead, the extra £725 you're asked to pay earns you a power drop of 41bhp. Not much of a bargain, you might think, but it means you're never going to get into a situation where the engine feels like it wants to snap the car in two.And there's a lot more to it than that. The 143bhp 1.6-litre turbo diesel engine is incredibly flexible, to the extent that it will operate quite happily from 1000rpm, just a couple of hundred revs above tickover. Extending it beyond 3000rpm is something of an extravagance, and one you don't need to indulge in even if you're trying to cover the ground quickly.Perhaps because of this (though with the extra help of a stop/start system which really does cut out the engine nearly ever time the car comes to rest, which is much less common than you might think) the Cooper SD is surprisingly economical. The official combined figure is 62.8mpg, and although MINIs in general have a reputation of being much thirstier in real life than they are on the EU test, this particular model comes closer to the ideal than most.Over the course of a week I averaged around 58mpg despite occasionally pushing the car quite hard. With a little care, 60mpg would be easy, 62.8 perfectly possible and 65 not unachievable. If you can't manage 50, either you're driving flat-out everywhere or you live in an area with an awful lot of steep hills.The engine is fairly noisy, but a lot of other sounds come in through the thin fabric roof so the effect isn't as irritating as it might be. A solid-roofed Coupé with the same unit the characteristic diesel rumble and clatter is much more insistent.I covered nearly 500 miles in this Roadster, and enjoyed it more than I thought I would. It's strictly built for two - there is nothing remotely resembling a rear seat - but it will happily accommodate a couple of large adults. The only reservation here is that, at six foot three, I found the top of my head was slightly above the level of both the top of the windscreen and the roll hoop behind me, which could get messy if the car turned over.But at least my skull wasn't constantly banging off a metal roof support, as is often the way with convertibles. In the Roadster, those supports are well-positioned, and several inches out of reach.There are still some interior space issues, though. The various seat adjustment levers are difficult to reach, and the ones controlling the angle of the seat backs are impossible to get to if the armrest is in such a position as to let you rest your arm on it.Still on the subject of the interior, MINI's insistence on copying the large central speedometer fitted to most (but by no means all) classic Minis has reached a ridiculous level. The speedo on modern versions is enormous, and so difficult to read that you're better off ignoring it and using the digital readout on the revcounter mounted right in front of you instead. The speedo's main function is to house information relating to the radio, air-conditioning, satellite navigation and so on, all of it much more clearly represented than the actual speed of the car.The incredibly quick response to steering inputs has been carried over from other MINIs, and that could be a bit of a problem if you tend to drive with your fists, since you may find the nose darting off more violently than you expected. This is a car that rewards a delicate touch.Several of the options fitted to the test car are available at no cost, by far the most useful being the small but effective wind deflector which is mounted between the roll hoops. Why would you not opt for that when you won't be charged for it?The category of options which do add to the price is much larger. The test car had no less than £6350 worth of them, including (but not limited to) the Chili, Sport and Media packs (the last of which includes satellite navigation), metallic paint, a very good Harmon Kardon audio system, metallic paint and - £215 well spent, I say - seat heating. Engine 1995cc, 4 cylinders Power 143bhp Transmission 6-speed manual Fuel/CO2 62.8mpg / 118g/km Acceleration 0-62mph: 8.1 seconds Top speed 132mph Price £21,630 Details correct at publication date