You know the scene. Somebody down the pub is droning on about what the Lotus Exige will do, giving it the usual bunny — 0-60 in 4.9sec, top speed 147mph, 189bhp, 41kg of aerodynamic downforce at 100mph, agile enough to outmanoeuvre a striking rattlesnake. In fact, he says, confident the claim will never be tested, it could probably even take on a hunter-killer helicopter gunship.

The audience at MPH will get the chance to judge the boast for themselves. Organisers are promising one of the most spectacular action entertainments sequences ever seen, in which a Lotus Exige is chased down by a helicopter in a furious ballet of smoke and missiles. Clearly getting a real helicopter to fly around inside Earls Court or the NEC would be impossible but with the help of computer technology the sequence is almost as convincing as the real thing.

Julian Napier, the man responsible for the $1m computer graphics (CG) sequences in Starlight Express, has been working on the sequence with a company called Sassoon. Like any magician he doesn’t want to give his secrets away but this much is known. First, you do need a screen, albeit one the viewer hopefully doesn’t see. It runs in an arc across the front of the auditorium and gives the car an action area of about 70 yards by 75 yards. Then you need projectors — a minimum of two, precisely aligned. One of Napier’s problems has been making the equipment effectively portable. Normally the projectors fill a truck and need to be set in stone.

The heart of the matter is a three-minute sequence of computer graphics, equivalent to 30 frames a second on film (normal movie speed is 25 frames a second), with the action doubled up for each eye. If you get it right, says Napier, the result is “a real live solid object, with mass, flying through the arena. The CG gunship looks every bit as real as the real Lotus Exige”.

The car’s actions are choreographed and much depends on Lotus test driver Gavin Kershaw’s ability to stick precisely to the script — and Jeremy Clarkson’s ability to follow suit. In the selfless pursuit of knowledge Napier has sat terrified in the Exige while Kershaw threw it through its routine, and he has the chiropractor’s bills to prove it.

“I was blown away,” he says. “It’s absolutely dreadful. He ties the thing in knots, with snap acceleration, braking like hitting a brick wall, and lateral g-forces that cause you to lose all control of your head. It’s violent, but Gavin can do it inch-perfect and under control every time.”

The car’s moves were laid down first and obviously depended on what was physically possible. No such problem with the gunship. Napier watched endless footage of manoeuvring helicopters, but he was able to take minor liberties with physics and aerodynamics in the interests of entertainment.

Does the car get away? The Exige is a lightweight mid-engined road-going racing car that puts so much state-of-the-art software between your foot and the wheels that it’s as far removed from the mass-produced metal on the road as the helicopter gunship is from the Tiger Moth. If you want to read about the circuitry, the brake cooling system or the aerodynamics that suck the Exige down onto the road you can get a brochure from the company, but suffice it to say that it goes like stink and looks the business.

And who cares that the whole contrivance is beyond belief? The fact is that a gunship like the Apache would no more chase a target up and down than a hunter would catch a rabbit by putting salt on its tail. You’d be dead before you knew it was coming. It wouldn’t need to do more than poke its radar dome, which can track 256 targets simultaneously and engage 25 of them within a minute, above a distant horizon. Its M230 chain gun will hit a target the size of the driver’ s door of an Exige at three miles with 625 depleted uranium shells a minute.

If it really wanted to get nasty it could unleash a barrage of Hellfire missiles that would take out the car, the audience, Earls Court or the NEC as well as their immediate environs in a fraction of a second.

The Exige provides as much protection as a brown paper bag and in the real world Gavin Kershaw would be toast. But hey, when reality and illusion collide, anything can happen.