What this then?
The most extreme version of Mercedes’ new AMG GT Roadster driven on UK roads for the first time. Mercedes will do you a cooking GT Roadster, but the GT C is the one you want. Taking the best bits from the AMG GT R – the wider track, four-wheel steer, electronic rear differential, adaptive sports suspension, toothy Panamericana grille, louder exhaust, lighter lithium-ion battery - and marrying them with a 549bhp version (28bhp less than the GT R, 28bhp more than the GT S and 80bhp more than the standard GT Roadster) of Merc’s twin-turbo 4.0 V8, it’s probably the most focused of the current R8 V10/Turbo S Cabriolet/F-Type SVR crop.

But, as we learned from the GT R, although the spec sheet reads like a track-special, it should be far more manageable on the road than the sum of its beefed-up parts. Question is, does more power, more bling, more noise, more everything necessarily mean more fun, especially on the UK’s uniquely narrow and crumbly roads?

It looks mean…
Yup, like some vast silken shark. Wider track and arches from the GT R, low, hostile, it looks spectacular burbling away in the morning light – you could probably park a more prosaic roadster, say an MX-5, on the bonnet alone. The roof is beautifully integrated to match the silhouette, but this isn’t about the details it’s about cartoonish proportions. We most definitely approve.

And do those proportions fit UK roads?
Right now we’re on Beachy Head Road, up early to beat the Saga tour buses, and it’s a game of damage limitation. It feels absurdly wide, wide enough for two accommodating seats, a fat centre console, and surgically enhanced wheel arches beyond that. The steering isn’t helping either, it’s on constant high alert. This is the definitive modern supercar steering set up: light on feedback, even lighter to turn (even in S+ and Race modes), but with a super-high ratio giving the front end a feeling of telekinetic responsiveness.

So the road, quite literally, isn’t a great fit for the GT C, but with an engine like this you’ll be amazed at what can be forgiven. You don’t need more than the length of your driveway to realise it’s a stonker, all gruff and woofly at idle – like it’s carrying up a nasty chest infection – but give it some revs and it makes all sorts of noises to keep you and your neighbours entertained. Forget Comfort and Sport modes, they’re far too tame, go straight for S+ or Race (not forgetting to dial back the suspension to the softest of its three settings) and the exhaust baffles open fully unleashing a snarling crescendo and a 21-gun salute when you lift off. With the roof down, it’s almost enough to justify the £139,460 price tag alone.

Enough performance to keep you interested?
There is a tsunami of acceleration, not that you can use it all on roads like this, but for a twin-turbo engine throttle response is superb, as is the snappy twin-clutch gearbox. In truth you find yourself short shifting at 4,500rpm because there’s just so much torque and no real benefits to wringing its neck, not on a track at least.

What about the ride, back-breaking presumably?
Au contraire. You have the option of Comfort, Sport, Sport+ and Race modes in the GTC, but then you can dial back the three-stage adaptive dampers separately. On UK B-roads this is excellent news as you can have the full baffles open and super-sharp powertrain experience in Sport+, but with the dampers in their most relaxed setting. There’s an underlying firmness, but it’s all beautifully damped so you’re never bottoming out, despite your bottom being suspended pretty much over the rear axle.

What about the roof?
It’s a whirring mechanical ballet of magnesium, steel and aluminium lasting eleven seconds and operational up to 48kph. Closed, the triple layer fabric is as virtually as refined as the coupe, open and buffeting is nicely controlled. One word of caution, if the attention a supercar brings with it is a concern, then a convertible amplifies it considerably. Sitting at the lights in coupe at least you’re largely obscured by glass and metal, but with the roof-down in the GT C you’re constantly on parade. I find myself not knowing what to do with my facial expression – do I grin like I’m the luckiest guy in the world and I know it, or do I go for something cool and sullen, whatever that looks like? Invariably I decide a straight-on middle distance stare and awkwardly drumming my fingers on the door is the way to go.

Enough posing, what’s it like when you’ve got a bit more room?
Deeply impressive. What you quickly realise is how rigid the reinforced chassis feels and how much you can lean on it through the corners. Where width was once the enemy, it now translates to indestructible lateral grip – honestly, you’ll need a racetrack to discover where it ends and the sliding begins. Four-wheel steering on the other hand is just brilliant at any speed – bringing a sense of agility to match that hyperactive steering, it’s like a couple of hundred kg have just been stripped away from the porky 1,735kg kerbweight.

A success then?
Yes and no. The GT C is overkill on UK roads, but Mercedes hasn’t taken any short cuts so it’s a car that feels indulgently over engineered for the simple process of clipping along with the wind in your hair. This is AMG at its very best, a full-on sensory overload, but really you need a race track to show what the GT C is capable of. And in turn, if track days are your thing we’d go for the GT R Coupe anyway…

- Jack Rix