Nicholas Longman, 46, of London Road in Aston Clinton, suffered spinal injuries when his silver Mercedes convertible collided with the Crows Nest roundabout off the A41.

His car is believed to have hit the roundabout at around 30mph causing it to take off before landing in the road on Tuesday, April 22 this year.

Rachel Carter was driving home along the bypass at around 8pm when she saw two cars driving at speed shortly before the crash.

During the inquest hearing in Amersham on Tuesday (September 2) Ms Carter read out her police statement. She said: "Two vehicles came to my attention because of their speed.

"Both vehicles took over me at speed, which I can only estimate as about 85 to 90mph."

She added: "It occurred to me that maybe they were chasing each other or racing."

She said the two cars overtook each other several times before the Mercedes left the bypass on the slip road.

"The car didn't stop and I watched as it collided with the roundabout flying into the air," she said.

The other car, believed to be a BMW, carried on along the bypass and has not been traced by police.

Paramedic and medical student Jonathan Careless, who was passing, stopped to try and help. He said: "At no time did I see any signs of life in the gentleman."

A post mortem examination revealed Mr Longman had an alcohol level of 243 milligrammes in 100 millilitres of blood, the legal limit for driving is 80 milligrammes.

Coroner Richard Hulett gave a verdict of accidental death and said that Mr Longman died from a fracture of the upper spine.

Investigating officer PC Alan McManus said: "The effects of alcohol on the ability of a person to drive are well documented."

He said on the day of the accident the weather was dry, clear and calm and that the slip road was in good condition and coated with a high friction surface.

During his investigation he found evidence that Mr Longman had strayed on to the hard shoulder of the slip road and had tried to correct the vehicle's position. He estimated the car was travelling between 49 and 60mph.

Mr Hulett said: "It seems as if he was travelling briskly and enthusiastically along the A41. He may or may not have been engaged in some sort of informal duel.

"He probably left the road a little bit later than he intended and then, as is so often described in this court, people find themselves in an over-steer situation."