AUDI'S A8 will join the burgeoning diesel luxury saloon brigade with a 4.0-litre V8 TDI in October, making it the most powerful car in its class in the UK.

Its 271bhp engine uses common rail technology and twin turbochargers, offering 479lb-ft of torque between 1,800 and 2,500rpm.

Audi claims the 0-62mph sprint can be achieved in 6.7 seconds, while top speed is limited to 155mph, with fuel consumption of 29.4mpg on the combined cycle. Mercedes-Benz has dominated the market in the UK with the S320 CDI, while BMW has just introduced the 730d.

Jaguar is expected to launch a diesel XJ next year, while Volkswagen's new Phaeton range will also include a diesel later this year. Prices and specification for the A8 4.0 TDI will be announced nearer to its launch.