Diana 1961-1997: The tragedy - Couple not wearing seatbelts in car goin g at more than 60mph

No car could have withstood the devastating crash which killed Diana, Princess of Wales and two other people early on Sunday morning, according to the vehicle's maker, the German company Mercedes-Benz.

The company said such a high-speed head-on collision with a solid object - a concrete pillar - was extremely rare, accounting for less than one per cent of automobile accidents worldwide.

"No vehicle in the world is built to withstand the dimensions of this accident," said Wolfgang Inhester, a Mercedes spokesman.

Experts who saw the damage to the car suggested it could not have happened at less than 50mph, and some reports said the car was travelling at more than 60mph when the accident happened.

The front of the vehicle folded like an accordion, its bumper was driven back almost to the windscreen and two inflated airbags were visible in the wreckage.

The roof was crushed almost down to the bonnet all over the car. Incredibly, the front passenger, bodyguard Trevor Rees-Jones, survived with "non life- threatening" injuries.

The internal injuries which killed Diana suggested a crash at more than 60mph, Mr Inhester commented. Neither Diana nor Dodi Fayed were believed to have been wearing seatbelts in the back.

But an American expert from a team which has studied car crashes for 30 years said that a crash at that speed would render rear seatbelts almost useless.

Lawrence Schneider, of the Transport Research Institute at the University of Michigan, said: "Even at 50mph you're getting to the speed where [back- seat] belts have limited use. And they won't do much if the car rolls over and the roof is crushed."

They are most useful in preventing people being thrown around the car, which can cause deadly injury. "Seatbelts are the first major point of protection to keep you in the vehicle and keep you from striking things in the vehicle," he said.

The Mercedes S-Class is the manufacturer's top range, with a starting price of pounds 70,000 and a top speed of 155mph. The luxury saloons are popular with top executives, celebrities and politicians.

The model involved was equipped with airbags for both the driver and front passenger. However, back-seat passengers only have their seatbelts to protect them in a crash.

Officials at Mercedes have offered their assistance to French accident investigators.