The McLaren 675 LT is Britain's 666bhp, 205mph cabrio

They’ve only gone and blown the bloody roof off. This is the McLaren 675 LT Spider, a 666bhp, 203mph V8 convertible that’s out to wage war on loose-fitting hats worldwide.

Woking calls it ‘the most focused, fastest and exhilarating open model to ever wear a McLaren badge’, and you’d be braver than us to argue.

The 675 LT Coupe, you’ll remember, was effectively a 650S turned up to 11, a car we described as perhaps the best McLaren since the F1.

Wisely, then, the 675 Spider doesn’t mess with the hardtop’s rather brisk mechanical formula. Under that slatted rear deck sits the same 3.8-litre twin-turbo V8, an engine with shares barely 50 per cent of its parts with that of the 650S.

As well as that devilish 666bhp produced at 7,100rpm, it makes 516lb ft of torque. Churning through McLaren’s seven-speed double-clutch gearbox to the rear wheels, that’s good for a 0-62mph of 2.9 seconds – a time identical to the 675LT hard-top – with 124mph reached 5.2 seconds later. By any standards, that’s heroically, ridiculously quick.

Because the 675’s carbon tub is so strong, McLaren says no extra reinforcement was required for the convertible. Which means the 675LT Spider remains light – with a dry weight of 1,270kg, it’s some 100kg more lissom than the not-very-heavy-at-all 650S Spider, and just 40kg heavier than the 675LT Coupe. Thank extensive use of carbonfibre for the bodywork.

The roof is McLaren’s favourite three-piece folding hard-top, carried over wholesale from the 650S Spider. It can be opened at speeds of up to 19mph, which would be helpful but for the fact it’ll prove all but impossible to travel as slowly as 19mph in the 675.

The suspension set-up remains identical to the 675LT Coupe, with a front track 20mm wider than that of the 650S, and stiffer spring rates from and rear.

The ‘LT’ in the name is short, of course, for ‘LongTail’, referencing 1997’s racing F1 GTR, which featured extended bodywork in pursuit of extra downforce and extra cool.

And yes, the 675LT Spider is fractionally longer than the 650S Spider, but it’s that fat rear airbrake that’ll do more to contribute to the 40 per cent increase in downforce here.

The 675LT Coupe sold out all but instantly, and expect the Spider to shift just as quickly. Production will be limited to just 500 cars globally, with prices starting at a very, very senior £285,450.

That’s a lot of money for something with all-but-identical power to the Ferrari 488 Spider, which is likely to clock in around the £200,000 mark.

But so sublime was the 675LT Coupe that the Spider might just justify its Premier League price tag. It arrives next summer.