It's a tense but thrilling moment in the development of any new car: the day on which its engineers finally hand the keys over to someone outside the project for a critical, independent assessment. For us at McLaren, that moment came at the end of January in southern Portugal, at the Autódromo Internacional do Algarve, known simply as Portimão. The global press drive won't take place until early summer but a small group of journalists from some of the world's most respected car magazines were invited to test our new MP4-12C on the track and surrounding public roads. The four cars at Portimão were still production prototypes, excused their duties from our exhaustive test programme at the IDIADA track near Barcelona; I drove one down to Portugal myself. I suspect that few car makers would have given the press access to their prototypes, but we felt that the cars were ready, and we knew that enthusiasts around the world were keen to find out how our new car feels to drive.

In this, our second e-briefing, we'll take you behind the scenes at the Portimão test, give you a sneak preview of what one independent expert thought, and reveal the views of another very special tester; someone used to driving one of the few cars that's faster than the 12C.

And today we're revealing the 12C's official performance figures. We're proud to bring you the news first, and I hope you'll be impressed. But the 12C has always been about more than simple, straight-line speed; our intention from the outset was to produce a complete, perfectly-resolved, high-performance sports car. At Portimão, we asked some of the world's toughest critics if we've achieved that. We were delighted by their response, but it's your reaction that really counts.

I had a Bugatti Veyron for a few months,' says Jenson Button. The Veyron is the world's fastest, most expensive car.
'But I wouldn't compare it to this. It just wouldn't be fair on the Veyron...'

The former world champion has joined Live and McLaren's engineers at the Portimao race circuit in Portugal for the final test of its new MP4-12C supercar. It won't be launched to the press until April, with the first customers taking delivery soon after.

But I'm about to test it, and we're the first to be able to tell you what this all-new British supercar from a new British supercar maker is like to drive on road and track.

Of course, you'd expect Button to be positive about the latest venture from the Formula 1 team that employs him. But his enthusiasm seems utterly genuine; uncontainable, even. He's already spent the morning driving the car and has had a long meeting with McLaren's engineers.