The BMW M6 Gran Coupe is truly rewarding to drive, thanks to well judged dynamics, a thumping engine and a thrilling rear-drive chassis. It just never feels quite worthy of its astronomical price. If you have the money, you won’t be disappointed – but Mercedes’ CLS63 AMG does a similar job for £15,770 less.

This new BMW M6 Gran Coupe means buyers searching for a big grand tourer packing serious performance are now spoilt for choice. The Audi RS7 and facelifted Porsche Panamera Turbo have arrived recently, and now BMW has thrown its hat into the ring with this four-door version of the M6 Coupe. This is our first chance to test it in the UK.

• BMW M6 Gran Coupe full review

The BMW M6 Gran Coupe certainly looks good, with the kind of head-turning muscle normally reserved for supercars. Under the skin it shares its 552bhp twin-turbo V8 with the BMW M5. Paired with the seven-speed M-DCT dual-clutch transmission and adaptive suspension, this allows the Gran Coupe to switch from supple cruiser to savage muscle car at the touch of a button.

Even on straight, dry roads the towering 680Nm of torque is enough to set the traction control light flashing in second and third gears. Turn the ESP off and you can steer  the car on the throttle – which makes it an engaging handful on the right road. However, on narrow lanes the size, weight and power restrict your ability to exploit the engine.

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You sit much lower to the ground than in the M5, and while this adds to the sense of occasion, reduced visibility makes pulling out from tight junctions a touch tricky. The sloped roof means passenger space in the back is tight, while the small 460-litre boot and four-seat layout make it less practical for long European tours than rivals from Audi and Mercedes.

The cabin is reassuringly plush, though, with carbon fibre dash inserts and sumptuous leather seats. Major switchgear like the steering wheel, stubby gear selector and shift paddles are all stylishly designed yet superbly functional, too.

But despite all the different set-ups for the gearbox, steering and suspension, the Sport Plus mode doesn’t offer much more dynamic flair than Sport, while even in the Comfort setting the car patters over broken surfaces.

Considering the performance on offer, the economy and CO2 emissions impress, matching those of rivals. But the two-door M6 is already expensive, and the £3,000 premium the Gran Coupé carries means it looks very pricey.

Our test model came with a raft of options, including carbon-ceramic brakes and ‘Individual’ leather, which took the price to £116,055. Buyers spending this much could go for something more exotic and more capable.