The key premium-brand rival for BMW’s new M135i saloon will be the Mercedes CLA45 AMG. Based on the same flexible platform structure as the latest A-class and B-class, the new style-led four-door Merc will crown the heavily anticipated CLA line-up. It will go on sale in the UK in early 2014 at a price of about £38,000. That’s £20,000 less than the similar-sized C63 AMG, which is itself set to be replaced by a bigger all-new model towards the end of 2014.

The CLA45 AMG will be the first Mercedes performance saloon to use a transverse engine layout. It will share its turbocharged 2.0-litre four-cylinder powerplant and four-wheel drive system with the smaller A45 AMG, which will go on sale in the UK next summer.

Mercedes insiders keenly describe the CLA45 AMG as a baby CLS63 AMG. Power peaks at a heady 349bhp, providing the range-topping saloon with a specific output of 175bhp per litre. Torque is said to be 332lb ft.

Drive is sent through an in-house-developed seven-speed dual-clutch gearbox, electronic differential and Haldex-style multi-plate clutch to all four wheels.

AMG won’t be drawn on official performance claims ahead of the car’s unveiling at the 2013 Frankfurt motor show, but insiders suggest that it will get close to 5.0sec for the 0-62mph dash, with top speed limited to 155mph in standard guise and rising to 168mph with an optional performance package.

Fuel-saving technologies, including brake energy recuperation and an automatic stop-start function, contribute to combined fuel consumption of more than 40mpg.

Previewed by the Concept Style Coupé at the Beijing motor show this year, the 4600mm-long CLA draws its heavily structured appearance and coupé-like silhouette from the second-generation CLS.

As with standard versions, the CLA45 AMG will be produced at Mercedes’ new manufacturing plant in Tecskemet, Hungary.