It seems appropriate to be reviewing this Focus in the same week that what lies under its bonnet won the 2012 International Engine of the Year award. The three-cylinder turbo petrol unit - at 999c the smallest Ford has produced in decades - is available in two forms, and the one under consideration here is, at 123bhp, the more powerful. There's also a 99bhp version which is £500 cheaper and offers better fuel economy.Still, the 123bhp (or 125PS) engine is quite economical too, and this, rather than what seems like an extraordinarily high power output from so few cc, is the whole point. The 1.0 EcoBoost is the new-generation equivalent of the 1.6-litre four-cylinder non-turbo engine which is still available in the range but only with Powershift semi-automatic transmission, and although the EcoBoost's straightline performance is similar its fuel economy, and therefore CO2 emissions, are simply in a different league.A Focus fitted with even the 123bhp engine has a combined economy figure of 56.5mpg and a CO2 rating of 114g/km. Annual Vehicle Excise Duty payments are therefore just £30, which is extraordinarily low for a petrol-fuelled car of this size.How easy or otherwise it is to match the official 56.5mpg figure remains to be seen. This was too short a test for meaningful economy figures, though we'll have another 1.0 EcoBoost soon and will make a point of investigating. If it doesn't, I'd be inclined to say that that's not Ford's fault, since this engine owes its very existence to the philosophy of downsizing and forced-inducting adopted by so many manufacturers to score well on the official test, which has practically no performance element at all and therefore favours turbo engines whose turbos are hardly required during it.Aside from all that, there are other reasons to welcome the 1.0 EcoBoost. For a start, it sounds lovely, as three-cylinder engines generally do, though at times you'd be hard-pressed to hear it; even when you accelerate on full throttle right up to the rev limiter (yes, I did that, twice, and I don't care who knows it) it never goes beyond mezzoforte.That same exercise also showed that the engine doesn't attain full steam until 4000rpm, but it produces maximum torque from just 1400rpm and is certainly useable at such low speeds, in a way that even some diesels were not until quite recently.One possible reason for this is that, very unusually for a modern engine, this one's stroke is 14% longer than its bore. (If that sentence doesn't make sense to you, don't worry - just a bit of geek talk.) Consequently it is also tall, which doesn't help the centre of gravity situation one bit, and furthermore it's not very much lighter than the four-cylinder 1.6 - certainly nothing like as much as the 1.6 is than the similarly-sized diesel.But the reduced weight does, and the tallness doesn't, seem to have an effect on the Focus's road behaviour. It's slightly easier to drive in town, thanks to marginally lighter steering, and it's much more fun on a twisting country road than I would have expected. In fact, in that respect it exceeds every other current-generation Focus I've driven, which just goes to show that there are more reasons to be impressed by its engine than because it allows you to withhold a small sum from the Chancellor of the Exchequer. Engine 999cc, 3 cylinders Power 123bhp Transmission 6-speed manual Fuel/CO2 56.5mpg / 114g/km Acceleration 0-62mph: 11.3 seconds Top speed 120mph Price £20,945 Details correct at publication date