How about this...
They're each given a thousand pounds to buy a hot hatch, any hot hatch. (don't tell them what it's for)
Once they've bought a car, they are then given an additional 500 pounds to fix up the cars any way they want (again don't give them any clues on what the competition is about).
Then they enter their "fixed up" cars in a Car Show (preferably one with alot of "youngsters") in which they have to drive their cars to the car show (make it far), points for whichever car gets the most attention/prizes, points are deducted for breakdowns on the way to the car show. Maybe make individual contests like who has the loudest stereo, who has the rims with the most "bling", and who has the largest exhaust pipe! :lol:
Finally, their cars are sold at an auction (rip off of fifth gear
) and they get a point for every 10 pounds over 1500 pounds they sell their car for, and they get deducted 1 point for every 1500 pounds they get deducted.