Rolls-Royce is returning to the convertible market for the first time since dropping the Corniche in 2002.

The BMW-owned luxury car maker will unveil its new Phantom 'Drophead Coupé' at the Detroit Motor Show on Sunday 7 January. Production of the new car will start at Goodwood, on England's south coast, next summer.

Although based on the Phantom limousine launched in 2003, the two-door, four-seat convertible has around 1,400 new parts and is described by its maker as "a less formal interpretation of classic Rolls-Royce design". The sharply raked nose is a first for a factory-built Rolls-Royce.

Rolls-Royce Motor Cars chief designer, Ian Cameron, said, "This car gave us the chance to think about the very nature of convertible motoring and in particular what it means to Rolls-Royce. Above all we were determined to make this car a joy to live with and engineered it to give years of effortless service to its owner."

A number of features first seen on the 100EX, the experimental convertible shown in 2004, have been engineered into the new drophead coupé. Two of the most visually striking of these are the brushed steel bonnet and A-pillar and the teak decking for the rear hood cover. The brushed steel is machine finished to give a uniform grain before undergoing extensive hand polishing.

At the rear, the teak decking is treated with a mix of oils to preserve a natural finish and a long lasting lustre. An annual polish is part of the service schedule.

Front opening 'coach doors' are the most unusual feature of the new car and, Rolls-Royce claims, add considerably to the ease of access to the rear seat. They also aid the overall stiffness of the body as the rear hinged doors allow for an uninterrupted A-pillar.

Luggage is housed within a 'picnic boot', a split tail compartment that opens in two parts giving easy access to the 315 litres of space. The lower tailgate provides a comfortable seating platform for two adults when lowered. The folding soft-top roof means that it stows in a relatively small space resulting in a luggage compartment that remains unaffected regardless of whether the roof is up or down.

The five-layer fabric hood is the largest of any modern convertible car and lined with cashmere.

Power comes from the same BMW-designed 6.75 litre naturally aspirated V12 engine used in the Phantom saloon.

Rolls-Royce chairman and chief executive, Ian Robertson, said: "The Phantom Drophead Coupé marks the next chapter in our history. While the saloon continues as the brand flagship, the Drophead leads us in a more informal direction, attracting new buyers to the marque. In the coming years other new models will strengthen the company still further."