We are on the set of a British comedy, yes? At any moment, John Cleese will appear and vent his anger on a box hedge. And then it’s all back to the knot garden where we shoot the love scene. No? Well, if this isn’t a film, then perhaps someone would be kind enough to explain what all those cars are doing.

They’ve been at it for an hour now, a fleet of BSM hatchbacks waltzing around the grounds of Sudeley Castle, home of Lady Ashcombe and her son, Henry Dent-Brocklehurst (he of the recent society wedding). It’s most bewildering.

Every so often, one of the cars will scrunch to a halt, the driver’s door will open and out will step a grinning teenager. Then another teenager will emerge from a rear door, mutter something like “I can’t believe I’m doing this”, and swap places with the driver.

The engine revs, the gravel flies (“I said ease gently up on that clutch pedal”), and the whole thing begins again. What on earth is going on? Iain Blaikie is the man to ask. He’s head of nearby Winchcombe School, a small foundation school a few miles out of Cheltenham, and it’s his Year 11 students who are burning all the rubber and giving the head gardener the heebie-jeebies.

Blaikie’s explanation of this extraordinary scene is simple: he’s trying to save lives.

He prudently steps back as yet another party of teenagers takes a short cut across the turf. “They are at that magic age between the youth club and the pub,” he says. “The car is a fashion accessory, and the one with the car is the hero.

“On a Friday night, six or seven of them will cram into an Astra or a Fiesta. Then it’ll be foot down along the dark, winding lanes, music blaring while the car fills up with smoke and alcohol fumes.” He is sick, he says, of turning on the local news and hearing about yet another head-on smash, wondering whether it will be his pupils this time.

“The other day, three 18-year-olds were wiped out in Walsall. We’ve had some horrendous accidents - we have one pupil in a wheelchair. The tragedy for the families is colossal. And so much of it is down to inexperience.”

It was with a view to mitigating the effects of this inexperience that Blaikie called in Young Gloucestershire. In 1998, this countywide youth charity developed its own version of Roadrunners, a car-awareness course devised by the National Association of Clubs for Young People with backing from Royal and Sun Alliance and Crime Concern.

The one-day course consists of five workshops, and for each of the 67 students taking part today the highlight is undoubtedly driving a real car around Sudeley Castle with a BSM instructor. But back on the school premises, there are other challenges on offer.

“One of the depressing things,” says Blaikie, “is that they’ll spend their weekends and evenings working in shops, saving up to buy their first car. They get themselves pound;2,000 and they think that’s it. But a lot of that will go on insurance, so they have to buy whatever they can afford.

“Honest John sees them coming, and before they know it they’re driving a death trap.” Today, the pat of “Honest John” is played by youth worker Colin Gourlay. With a woolly hat pulled over his ears, he is out in the playground, pretending to sell an old banger to a dozen teenagers who aren’t quite sure what to make of him or his car.

One lad has already agreed to give him the pound;350 he’s asking. But is it a good buy? Gourlay stops acting now, and starts dishing out some sound advice.

“I bought this car for pound;300 six months ago,” he says. “It goes. It gets me places. It’s been to Scotland and back a few times. It’s also passed its MOT. If I’d spent pound;1,000 on something that does the same things, I’d be pound;700 worse off, wouldn’t I?” Peer pressure, he says, may steer youngsters towards more fashionable cars, but safety and cost are more important than stereos and go-faster stripes.

“It might not look flash; it might have a dodgy interior and smoke a bit; you might struggle to get it started in the morning. You must expect all that for pound;350. But it’s a car, it’s legal, and it’s the only one you’ve got. So at the end of the day, if you approach buying a car intelligently, get the help that you need - don’t try to do the cool guy thing, kicking a few tyres like they do on the movies - you’ll end up with something that’s worth what you’re paying.”

As the group heads off for the next workshop, Gourlay taps the faded bodywork. “Remember,” he tells them, “this is the most dangerous thing you’ll ever be close to.”

But they are already beginning to suspect as much. A couple of hours ago, they had a fire crew showing them how they go about cutting crash victims from a wreckage. Then there were the pictures the ambulance people brought along - “none too pleasant” is how Blaikie describes them.

Last session of the day is a giant board game, set up along a couple of rows of desks. It’s called Street Wise, and it’s about that thorniest of all issues for the teenage motorist: insurance. Each pupil starts out with pound;3,500 and a die to cast. First they pick a car (old or new, big engine or small), then they choose their insurance (comprehensive or the bare minimum). And they’re off!

Along the way there are accidents and fines, pay packets and lottery wins. “Third party pays for damage to the other person’s car,” a youth worker is telling one disbelieving girl. “But it won’t pay for the damage to yours, you know.”

By the time they reach the finishing line, most of these players will have lost every penny. And the hope is that they will have lost a few illusions along the way as well.

Not that the aim of the exercise is to extinguish their enthusiasm for the car, says Blaikie, but rather to make sure that their enthusiasm doesn’t literally run away with them. “The idea,” he says, “is that they will appreciate the breadth and variety of dangers involved in motoring and not go on to be the next victims.

“The accident statistics make grim reading. In the 17-24 age range, only 16 per cent hold a full driving licence. Yet these kids account for 34 per cent of car-related casualties. This is frightening and depressing.

“What begins as a good laugh can shatter lives, including those of innocent drivers coming the other way. This scheme is an aspect of citizenship, and worth all the time and effort if it saves lives.”