What's it like?
The 2.0-litre turbocharged four-pot might not have the melodic warble of the RS3’s five-cylinder motor, but when you turn up the engine modes - which opens the exhaust butterflies - it emits a very satisfying BTCC-like bark, with crackles on the overrun. It's blessed with a delightful mechanical smoothness right across the rev-range, too.
As a reference point, the A 45 is just 1bhp shy of the iconic Lotus Carlton (which some people screamed should be banned back in 1991 for being too powerful), so it should come as no surprise that this baby AMG feels quick. However, it never feels scarily quick, and that’s probably down to how effectively it puts down its power and how well sorted the chassis is.
As you come barreling up to a corner and jump on the brakes the pedal gives you all the reassurance you need as the A 45 sheds speed effectively. Turn in and the steering has the lovely weight and sense of urgency that only the best hot-hatches can muster.
With the adaptive dampers set to firm the body control is also superb, but with enough compliance in hand to keep the A 45 composed even when goaded by mid-bend undulations.
In the dry and with the optional limited-slip diff in place, the traction is prodigious. Even when the turbo on full song all four tyres seem to cope, managing the task with minimal fuss. Wet roads are a little more challenging, but in general any drama is limited to easily controllable understeer.
What’s good about the A 45 is that it still manages a decent degree of comfort when you dial everything back. It's firm, but never harsh, although it can't quite match the suppleness of an RS3. Meanwhile the gearchanges switch from snappy paddle-operated manual shifts to gliding pretty smoothly between the ratios in full auto mode.
The driving position is fine, the electric bucket seats fit like a glove, and even though this is the most junior of AMGs, the interior feels more solidly built than some of the more expensive models. It’s just a shame the infotainment system seems so far behind the Audi’s MMI system.
Should I buy one?
If we set aside the argument about the Golf R being almost as quick and £10k cheaper, which one should you buy out of the AMG A 45 and RS3?
Well, they’re both pretty awesome things, but if you need your weekend toy to double also as a full-on commuter/ family car, take the RS3. However, if it will sit in the garage simply waiting to make you smile on a Sunday morning blast, it's the A 45 that'll make your grin wider and last longer.
Mercedes AMG A 45 4Matic
Location Surrey; Price £39,995; Engine 4cyls, 1991cc, turbocharged, petrol; Power 376bhp at 6000rpm; Torque 350lb ft at 2250-5000rpm; Gearbox 7-speed dual-clutch auto; Kerb weight 1555kg; Top speed 155mph; 0-62mph 4.2sec; Economy 40.9mpg (combined); CO2/tax band 162g/km, 27%; Rivals VW Golf R, Mercedes-Benz A-Class, Audi RS3