Details of the new BMW 4 Series Convertible have been released ahead of its official on-sale date of 8th March 2014.

Based on the BMW 4 Series Coupe, the Convertible is lower, wider and longer than the previous 3 Series Convertible.

The 4 Series Convertible will initially be available with a choice of two petrol engines and one diesel.

The 428i Convertible, despite its name, is powered by a 2.0-litre four-cylinder turbocharged petrol engine that develops 245 hp at 5,000-6,500rpm and 350Nm of torque between 1,250-4,800rpm.

It can accelerate from 0-62mph in 6.4 seconds and on to an electronically-limited 155mph top speed.  When mated to the company’s eight-speed automatic gearbox, combined fuel consumption of 42.8mpg and CO2 emissions of 154 g/km can be achieved.  With a manual transmission, economy drops slightly to 41.5mpg and emissions rise to 159 g/km.

The most powerful model in the range initially is the 435i.  Power comes from a 3.0-litre straight-six outputting 306 hp between 5,800-6,000rpm and peak torque of 400Nm from 1,200-5,000rpm.  This equates to a 0-62mph dash of 5.6 seconds and a similarly electronically-limited top speed of 155mph.

Manual models achieve 34.9mpg with CO2 emissions of 190 g/km, while the auto version records 37.7mpg and 176 g/km.

The sole diesel engine of the range is to be found in the 420d Convertible, with 184 hp at 4,000rpm and 380Nm of torque between 1,750-2,750rpm.  0-62mph is dealt with in 8.2 seconds, with a 146 mph top speed.

Economy is the 420d’s strong point, recording 58.9mpg when mated to the eight-speed auto, or 55.4mpg with the six-speed manual.  CO2 emissions are 127 g/km and 133 g/km respectively.

The folding metal roof can be raised or lowered in 20 seconds at speeds of up to 8mph.

With the roof raised, the boot provides 370 litres of luggage space, dropping to 220 litres with the roof lowered.

The front seats feature integrated retractable seat belts, as well as electric adjustment and Dakota leather upholstery as standard.

Also standard are front and rear parking sensors, heated front seats, Xenon headlights, DAB digital radio, cruise control, and iDrive controller with a 6.5-inch colour screen.

Five trim levels – SE, Sport, Modern, Luxury and M Sport – offer subtle variations in equipment and appearance.  The M Sport model, for instance, includes side skirts, front apron and a rear diffuser.

The new BMW 4 Series Convertible goes on sale on 8th March 2014, priced from £36,675 for the 420d, £39,515 for the 428i SE and £44,970 for the 435i Luxury.