Even though the two-door has left behind its roots as a soft-top, it is keeping the original Convertible name, shunning a fancy CC-style title. Despite that, major changes to the design and specification mean the model is set to pose a serious threat to prestige rivals such as the Audi A4 and Volvo C70.

That's because the new arrangement provides the sun-seeking 3-Series with a big boost in refinement and desirability. The electrically operated three-piece lid is made out of lightweight steel, and the manufacturer claims that it delivers class-leading visibility and rigidity.

It takes 22 seconds to switch from coupé to cabrio, and the roof panels blend almost seamlessly into the distinctive bodywork. Elsewhere, unique headlamps and a revised bumper give the nose a noticeably different look to other 3-Series variants. Described by company bosses as an "undiluted re-interpretation" of the original Convertible, the car appears long and low, with a tall shoulder line that wraps the driver in the leather-trimmed interior.

The seat height has been reduced and the windscreen extended to improve visibility and make occupants feel even more secure. Some extremely clever technology has been added to the cabin, too. Top of the list is a new treatment for the leather seats - it reflects sunlight, and keeps the fabrics cool in the summer. There's also an electronically control­led rollbar which deploys in milli­seconds in the event of an accident. On the practicality front, the boot features a maximum load capacity of 350 litres; with the roof open, there's 210 litres of space. And, unusually for a cabrio, an optional ski hatch is available.

Under the bonnet, buyers will have a wide range of petrol and diesel engines to choose from. The 155mph flagship is fitted with the new 3.0-litre twin-turbo motor. This boasts 306bhp, and BMW says it's capable of returning 28.5mpg.

Two non-turbo 3.0-litre models are badged 330i and 325i respectively, while entry-level cars will be powered by the 170bhp 2.0-litre four-cylinder engine and titled 320i. There's one diesel, the 330d, which uses BMW's acclaimed 231bhp 3.0 motor. Delivering 500Nm of torque and capable of 152mph, this six-cylinder version is nearly as fast as the top petrol model, yet returns 40.9mpg.

Prices for the Convertible have still to be confirmed. However, it is expected to be around £2,000 more expensive than the 3-Series saloon, with entry-level cars costing from £26,000.