Vauxhall's new Astra cabrio has been spied in testing ahead of it reaching UK showrooms in 2012.

The firm recently confirmed plans to ditch a retractable metal roof for its forthcoming Astra convertible, and revert to the traditional electric “ragtop” principle it used successfully on previous models.

A sketch of the new drop-top Astra issued by Vauxhall’s British design boss, Mark Adams, showed a luxurious-looking bright-metal surround for the perimeter of what appeared to be a pure four-seat cabin layout.

See the spy pics of the new Astra cabrio

The convertible has the same wheelbase and underpinnings as the saloon, but appears to have an extended rear overhang, allowing space both for a bin to contain the retracted roof and a good-sized, unfettered boot space.

Vauxhall is already selling five-door hatchback and (British-made) estate versions of its new Astra, and recently took the wraps off showroom-ready editions of its racy GTC three-door, on sale in British showrooms by November.

Read the full story on the new Vauxhall Astra GTC

A metal-roof TwinTop convertible has been part of Vauxhall’s range since the mid-2000s, but sales have been slow. GM Europe engineers believe the materials and know-how needed for efficient fabric roofs have improved sufficiently to overcome the twin traditional bugbears, noise at the motorway cruise and long-term durability.

Compared with a TwinTop the new convertible will be lighter, simpler and cheaper to manufacture, but Mark Adams’ designers are understood to be especially pleased that the need to accommodate a metal roof no longer compromises the rear lines of an Astra model that is supposed to sell on its beauty.

See all the latest Vauxhall Astra reviews, news and video