World champions McLaren suffered a massive embarrassment yesterday when their new Mercedes-powered MP4-14 car failed to complete its first test lap.

Just three hours after McLaren's 1999 Formula One car was unveiled to the world's press by Mika Hakkinen, his team-mate David Coulthard took it out on the track.

Hundreds of international reporters and cameramen watched the British driver disappear into the distance - and were astonished when a sudden silence replaced the sound of the engine and the car failed to return to the pits.

When it arrived finally, it was being towed by a breakdown vehicle with Coulthard sitting at the wheel. Electrical failure was suspected.

In their anxiety to cover the car, team members managed to shroud both the vehicle and its driver.

Earlier, team chief Ron Dennis had feared that the car's debut run could be problematic - it was certainly rare for a team to run an untried model in public.

"This car has got the smallest number of carry-over parts ever known on any McLaren car," he said. "Less than 10 per cent of it is from the old car. That is the biggest number of new parts we have ever had."

He and chief designer Adrian Newey were anxious not to reveal the theory behind the ground-breaking new vehicle which is expected to maintain the team's domination of the sport.

"That is our secret and our advantage and we hope to keep it that way," said Dennis.

Hakkinen won the world drivers' crown and McLaren the constructors' championship last season.

The car boasts an all-new V10 engine, new oil and hydraulics systems and seven-speed gearbox, plus many other "under the skin changes", according to Newey.