Audi's tax-free A1

Audi has just unveiled a revised version of its A1 supermini that is both cleaner and more fuel-efficient than before.

Wait! Come back! This is important news, because in the battle for sub-99g/km-of-CO2 tax-dodging posh hatches, these differences make all the, erm, difference.

The revised 1.6-litre TDI four-pot in the A1 now returns a claimed 74.3mpg and emits 99g/km of CO2, meaning Mr Osborne can't pilfer any road tax duty (from the second year onwards), and Mr Johnson can't charge you for driving in his city.

Audi has tweaked the fuel system and ECU to achieve these money-saving gains, along with start/stop and energy recuperation systems. Though not at the expense of performance: 0-62mph remains the same at 10.5 seconds.

All rather boring but useful facts, correct? Only these economy figures are EXACTLY the same as the Mini One D. In fact, this A1 even costs the same as the Mini One D, at £14,480. The only difference is the standing start: the A1 has the jump on the Mini's 0-62mph time by 0.9s.

Then there's the small matter of the Citroen DS3 e-HDi, which emits 95g/km of CO2, returns 78.5mpg and will hit 62mph in 12.5 seconds (£14,600). Or the Fiat 500 TwinAir, which, at just 10,865 of your finest British pounds will give you 68.9mpg, emit 95g/km of CO2 and hit 62mph in 11 seconds.

We leave it to you, TopGear.commer, to decide which one you'd pick as your econo-box of choice...