He'd have been better off arriving a few hours earlier, because by 6pm mater was invariably on her fourth brandy. I'll never forget the look of horror on the poor chap's face when she insisted on a test drive before signing for it, but he climbed aboard anyway while I scrambled, excitedly, onto the clear plastic of the back seat before mother settled in behind the wheel and inserted the small, square-ended ignition key (serial number FS911).

"I worry that 95 horsepower just isn't enough," she opined, selecting her customary second gear before pulling away down the drive.

Once on the road, the youth's mutterings about 'running in' went unheeded as third was deftly engaged and the two-litre engine was taken to the amber line (but never the red), causing him to turn in his seat, gripping the fluted, chrome door handle with his right hand. "Vous ne parlez pas Français, my dear? 'Vitesse' means speed, you know…"

It certainly seemed swift at the time, but things have moved on a bit since then, which is why I'll always be grateful that mother never got her hands on Bugatti's latest creation, also labelled the Vitesse – or, to be absolutely correct, the Veyron 16.4 Grand Sport Vitesse.

The 'GSV' is, quite simply, the quickest convertible on earth, marrying the open-top Grand Sport with the beefed-up, Super Sport engine. I'll get the numbers out of the way now: a claimed 1,200 horsepower; 1,100lb ft of torque from 3,000rpm; 7,993cc W16 engine; four turbos; top speed of 256mph (or 235 with the lid off). Oh, and 1.65 million euros – plus tax.

Forget wind-in-the-hair motoring. This is typhoon-in-the-toupé stuff, about the nearest you can get to flying on the ground without being in the cockpit of Thrust SSC.

The Veyron is already an automotive legend, but the GSV could be regarded as extra special because, we are told, this is the last of the line. All 300 closed coupés are now sold, and production of the designated 150 open cars is well advanced, with 59 already spoken for, 13 of which (at the time of writing) have been ordered to Vitesse spec.

An open top seems logical for a car such as the Veyron which, one would expect, is invariably going to be used in sunny climes. Having never driven the 'cooking', 1,001 horsepower versions I can't compare the performance – but the 1,200 horsepower of the GSV with the lid off gave me the sort of adrenalin rush I've only ever felt at the controls of a superbike.

On full (well, quite full) acceleration, the car actually feels as though it might lift its front end off the deck – but that's never going to happen, of course. Bugatti's boffins have seen to that, with new coil-over, gas suspension which drops the car to a mere 3.5 inches off the road in dynamic mode, the double diffuser on the back (which automatically compensates for a change in airflow with the roof off) and various other aerodynamic tweaks that keep everything well and truly on terra firma.

Much has been made of how easy the various Veyrons are to drive 'normally', with light controls, easy steering, a smooth-changing gearbox and an ability to potter which is almost as difficult to comprehend as their performance statistics at the upper end.

But the GSV is in no way anodyne. Flooring the throttle produces a magnificent symphony from the V16 behind your head, accompanied by an interesting cacophony of sucking and blowing from the four turbos which is reminiscent of some giant steam press being put to work.

Overtakes are, of course, effortless and it's easy to forget that the sort of increase in engine revs that would perhaps cause slight acceleration in a conventional-performance car results in scorched-earth progress in the GSV. To put that into context, zero to 180mph takes just 16 seconds and the quarter mile is 'dismissed' (as the old motoring mags used to say) in just 10.

Driving the car on fabulously empty and temptingly curvaceous Spanish country roads did much to reveal what an achievement the GSV is – although I was, of course, grateful for the opportunity to breach the 'double ton' on a private proving ground, an event which happened so easily it barely warrants mention.

In the enviro-conscious, hybrid era in which we have found ourselves since the Veyron's mooting a decade ago, will there ever be another vehicle like the GSV? A purely petrol-powered, open-topped hypercar with the engineering integrity of a space rocket? It seems unlikely, so you should get yours while you can.

After all, there are only 91 left. Probably 90 by now. Maybe even 89...

Photos: Bugatti