Crewe, England  - Prestige car-maker Bentley has introduced what it describes as its most powerful convertible ever - the GTC Speed fitted with a 610 horse power engine, giving it a top speed of 322 kilometres an hour with the roof up.

To emphasize its sporty credentials, the GTC Speed features larger 20-inch multi-spoke alloy wheels. The radiator and lower-air intake grilles feature a standard, dark-tinted matrix.

Wider twin-rifled exhaust tail pipes and a new boot-mounted lip spoiler providing better downforce at high speed.

"The GTC Speed completes the family of Continental Speed models and broadens the appeal of the GTC to customers who demand a more focused, open-top driving experience," according to Bentley chief executive Franz-Josef Paefgen.

The six-speed transmission can be left in two fully automatic modes (Drive and Sport) or used as a clutch less manual to allow the driver to change gears sequentially, via either the gear lever or paddles behind the steering wheel.

Bentley claims that improved body control reduces pitch and roll when taking corners. The cabin interior is available in six natural, unbleached, laser-cut wood veneers and 17 premium grade leather hides.

It features diamond-quilted hide seats with embroidered Bentley emblems, a chrome and hide gear lever and a three-spoke multi-function steering wheel with brushed aluminium switch surround.

Options include follow-to-stop, radar-based Adaptive Cruise Control (ACC), fade-resistant carbon ceramic brakes and a premium audio system with iPod/MP3/USB interface.

Bentley was founded in Britain in 1919, but bought out by the German carmaker Volkswagen in 1998. (dpa)