The spies have been out spotting the next-generation Audi A4 which is due for release next year. On the outside its styling is pretty similar to current Audi models, but under the skin it is expected to be radically different and incorporate many construction materials that will challenge accident repairers.

The new A4 will be the first to have the new 2.0-litre four-cylinder TFSI Audi engine which is said to offer high power levels combined with 56.5mpg. A plug in hybrid model will also be available.

It is the structure of the vehicle that is said to be one of its biggest changes in the race for the benefits of reduced weight. It uses a new VAG Group MLB platform (Modular Longitudinal Matrix) which has been five years in development and moves away from the traditional welded steel monocoque structure. Instead the A4 will utilises a mix of aluminium and steel, with lightweight composite materials also being introduced. This will all be held together by rivets, screws and advanced adhesives.

Audi engineers believe using different materials for different parts means a more optimised structure and are prepared to invest in this theory with a complete retooling of the A4 production line required.

Latest thinking is that the A4 will use high-strength steels for the sills, body pillars and crash structures at the front of the car. Parts of the engine bay, front suspension turrets, roof panels, bonnet and front wings will be made from aluminium. Composite materials are expected to be utilised in later versions of the MLB platform.