The all-new Audi A4 has been spied testing for the first time ahead of its 2015 launch. The new four-door saloon was caught in a heavy disguise on the back of a lorry close to Audi's headquarters in Ingolstadt.

New saloon and Avant models of the A4 are due to reach the UK in April 2015, with an Allroad variant to follow later in the year. Successors to the A5 coupé, cabriolet and Sportback will follow in 2016. 

The car has been styled under the direction of soon to depart Audi design boss Wolfgang Egger. Insiders privy to the final design say it will be evolutionary, albeit with heavily updated detailing.

Distinguishing features include a newly styled 3D-effect single-frame grille, trapezoidal LED headlamps, more heavily creased bumpers and a prominent shoulder line running the length of the flanks. Sharper creases will also feature on the bodywork.

Dimensionally, the new model is reported to remain close to the existing A4, somethign backed up by these initial spy pictures. Luggage capacity is said to increase slightly to around 490 litres, but plug-in hybrids get a slightly smaller boot due to the mounting of hybrid components.

The new A4, codenamed B9, is also set to become the first conventional steel monocoque Audi model to use the company’s MLB (modular longitudinal architecture) platform to significantly benefit from a range of weight-saving initiatives, including aluminium panels. Sources report a 100kg reduction in kerb weight for the base-level A4, droppping it to 1330kg.

The engine line-up for the new A4 will encompass a wide range of four-cylinder and six-cylinder petrol and diesel units. Cylinder deactivation is also likely to be offered on a wide range of engines.

Petrol engines are expected to include 140bhp 1.4, 180bhp 1.8 and 220bhp 2.0 four-cylinder units and a supercharged 3.0-litre V6 with 310bhp, boosted to 340bhp in the S4. Diesel engines are likely to be a 105bhp 1.6, a 2.0 in 150bhp and 180bhp guises and a 3.0-litre V6 giving a choice of 220bhp and 270bhp.

Audi will also offer the fifth-generation A4 with three new plug-in hybrid drivetrains. The move is a bid to pitch the model as the most high-tech and fuel-efficient car in the fiercely competitive compact executive segment.

Petrol-electric and diesel-electric plug-in hybrids will be offered in the new BMW 3-series rival, featuring latest-generation four-wheel drive, eight-speed automatic gearboxes and an electric-only range of up to 31 miles.

Audi has three plug-in hybrid drivetrains under development, all based around a common electric drive arrangement that uses a 110bhp electric motor housed within the gearbox casing. Engines to be mated to the technology include the 220bhp 2.0-litre petrol, 180bhp 2.0-litre diesel and a 250bhp version of the supercharged 3.0-litre V6.