And with temperatures...

And with temperatures on the frozen Swedish lake plunging below -10oC, it"s no wonder the test driver decided to keep the fabric roof firmly closed. But despite this, it"s still possible to see how the heavily disguised prototype is shaping up. Although the car will have broadly the same look as the four-door saloon, changes have been made to the proportion and size of the body to make the most of the new design.

The bonnet, however, remains virtually identical, as does the front light arrangement. At the back, expect bigger changes. New rear lights take centre stage, and there"s a shorter boot which has been designed to neatly swallow the electric folding roof.

Details of the engine range remain a closely guarded secret, but the line-up is widely expected to include 1.8 and 2.4-litre petrol units, as well as a new 2.0 diesel for high-mileage company car motorists. The front-wheel-drive machine will also offer a choice of five and six-speed manual gearboxes, as well as a new semi-automatic, currently under development. In addition, the C50 cabrio is said to share its platform with a new high-performance C50R, rumoured to offer all-wheel drive and at least 300bhp.