It must be a constant irritation to the staff at McLaren Automotive to hear people suggesting that McLaren’s lack of form on the racetrack is in some way connected to all the resources being poured into its road car programme. The truth is, the companies that make the road and racing cars are entirely separate entities, with a headquarters, corporate identity and very little else in common.

So while you’ll not need me to tell you about struggles McLaren is having on the circuit, the good news for fans is that the road car business is both profitable and expanding. When you consider it only became a full-time car manufacturer four years ago and that its first product – the MP4-12C – got off to a poor start by being launched before it was ready and with indifferent styling, that is some achievement.

In fact, if you were to drive this new 675LT and then think back to the 12C, you might be close to staggered to see how far this company has come in such a short period of time. The first time I drove a 12C was as part of an annual competition for another publication to discover the identity of Britain’s best driver’s car and, I kid you not, it came in behind a Vauxhall Corsa.

By contrast – and if you except the million pound hypercars – the 675LT is probably the most capable supercar to deploy across road and track environments I have ever driven. Indeed if you read the mainstream motoring media, you will doubtless come across those who say it’s better even than the titanic 903bhp McLaren P1 hybrid, because it is so much lighter. It’s not a view I’d go along with myself, but I understand and respect it entirely.

In essence, the 675LT (for longtail, even though it doesn’t have one) is a 650S granted an additional 25bhp, a mammoth 100kg weight loss programme, suspension stiffened a fair bit at the front and a whole lot at the back and bespoke Pirelli Trofeo R tyres, described to me as halfway between a slick and standard street rubber.

If you want to understand how difficult it is to reduce the weight of a car whose tub is already made from carbon fibre by such an immense amount consider that when Ferrari was turning the aluminium 458 into the Speciale it banished the music system, the navigation and even the carpets to the options list and still only saved 80kg. The 675LT retains them all.

Even so, the list of modifications specifically aimed at saving weight runs to over 110 lines of spreadsheet. Some of the more notable savings include carbon fibre bodywork aft of the doors, thinner windscreen glass, a Perspex engine cover, lighter wheels, less sound deadening, a simplified wiring loom, a titanium exhaust system and so on.

With the extra power, an even quicker gearshift and completely revised suspension, the effects are devastating. In incremental terms, it’s like getting out of a bog standard 911 and stepping into a GT3, except here the starting point is already a car that will keep up with a McLaren F1 up to 100mph…

On Silverstone’s Hangar Straight the LT would show 160mph with ease before Stowe, not by catapulting out of Chapel on the Grand Prix circuit, but entering at a comparative crawl from the abbreviated International circuit. And when you got there those suspension changes, not to mention three times the downforce, meant the car was actually far easier to control into the apex and happier to nudge its tail out at the exit.

But that’s not this car’s real achievement. Where it breaks new ground relative to any comparable car is that it remains eminently and enjoyably usable on the road. Its ride quality is still superlative, its body control inexplicable to a man with a brain as small as mine. It’s noisier for sure, but would I take mine away for a two week driving holiday? I don’t think the question would even enter my head: it’s good enough to use as a daily driver.

Not, of course, that many if any owners will do that. The 675LT is not just crazily fast, clever and special, it is also extremely rare. McLaren said from the outset it would only build 500 (it made 375 P1s) and all sold for £259,500 long before a customer got to drive one. McLaren now knows it could have sold many more than this and while the bean counters are probably kicking themselves, the marketing types are quietly pleased because they know that for demand to so outstrip supply will do the brand no harm at all.

For a marque barely out of nappies and still recovering ground lost in a difficult birth, that matters far more than a few extra short-term sales. Expect classified ads for unused second hand cars before the end of the year and if you’re not prepared to part with a figure beginning with a three, I suspect there’ll not be much point looking.