The new A45 will also get a significantly wider front track and receive its own unique wheel carriers in a bid to reduce unsprung mass. It will roll on standard 18in wheels, but 19in rims will be an option.

The basis for the changes to the M133 engine unit comes from Mercedes’ new M260 four-cylinder engine. This is derived from the older M270 motor used by today’s A-Class but has a new crankcase and cylinder head.

Initially, the reworked M133 will feature a traditional exhaust gas-driven twin-scroll turbocharger. However, AMG is also developing a more advanced variant of its new engine that uses a 48V electrical system and runs both an electric-driven turbocharger and electric motor in a hybrid set-up that promises an even greater ramp-up in performance.

AMG is also looking to endow its new hatchback model with an extra 20lb ft — a move that, insiders have told Autocar, will provide it with at least 369lb ft and allow its 0-62mph sprint to crack the 4.0sec mark.

The changes to the A45’s driveline extend to its gearbox and multi-plate-clutch four-wheel-drive system. Both have been extensively redesigned to handle the higher torque loadings of the new model.

In line with developments further down the new A-Class line-up, AMG’s new flagship hatchback model is set to adopt a new nine-speed dual-clutch transmission, together with a faster-reacting four-wheel-drive system that offers greater variability in the drive split between the front and rear wheels, plus a torque vectoring function for added on-the-limit handling delicacy.

The new A-Class, which is codenamed W177, will have the most comprehensive AMG range thanks to the introduction of the Golf R and Ford Focus RS-rivalling A35, which was revealed at Paris motor show. That car faces BMW's next 1 Series hot hatch, which is set to adopt all-wheel drive and be called the M130iX.

“We’ve identified a market for a milder AMG model positioned below the A45 4Matic,” AMG boss Tobias Moers told Autocar. “The strategy is going to be similar to that seen further up the line-up, where our various 43 models support the 63 models.”

The new A45 builds on the developments of the new fourth-generation A-Class. The model is the first of up to eight new compact cars, which include replacements for today’s B-Class, CLA and CLA Shooting Brake, as well as the GLA. There will also be an A-Class Saloon (and its own 400bhp A45 variant), a GLB and a possible new seven-seat version of the GLB.

Additional reporting by Sam Sheehan and Andrew Frankel