A father who suffered a debilitating disease died when his car veered across a road and collided with a lorry.

Kenneth Jones, 37, of Dean Butler Close, Wantage, was killed on November 21 last year on the A420 near Shrivenham, when his Toyota Aventis car drifted across the carriageway into the path of a heavy goods vehicle.

At an inquest into his death, held at Oxford Coroner's Court on Tuesday, assistant deputy coroner Richard Whittington heard Mr Jones died instantly of multiple injuries. The lorry driver was not seriously injured.

Mr Jones had been suffering from the onset of Parkinson's Disease, which had caused him to give up his job as a businessman. It caused him pain and muscle cramps in his feet and difficulties with the left side of his body.

His wife Debbie, mother of their young son and daughter, told the court it was his birthday and he was on his way to go shopping to spend his birthday money.

His GP Dr Rickman Godlee said: "There was no particular reason to suppose that his medical condition contributed to his accident. He could drive perfectly OK. He was a relatively young person to have Parkinson's Disease and he handled it with as much grace as he was able."

But Prof Ralph Gregory, of the John Radcliffe Hospital, said: "The disease itself can make you sleepy and the drugs he was taking can cause sleep attacks."

Roy Wolfe, of Kingston Bagpuize, who was driving behind him, told the inquest that the Toyota drifted across the carriageway without any signs of braking.

He said: "It seemed like an unintentional drift, as if he was distracted by something and just took his eye off the ball. He could have fallen asleep, I don't know."

Mr Whittington recorded a verdict of death by misadventure. He said: "We still do not fully understand how it was that his vehicle came to be on the wrong side of the road. It seems it was quite a normal day. You (his wife) had gone to work, the children were at school he had gone to do shopping and was driving on a road he was familiar with.

"We know he was suffering from the misfortune of Parkinson's Disease, this particularly affecting the left side of his body.

"He did have a tendency to fall asleep and there's a feeling of probability that his medical condition in some way may have contributed to the circumstances of this fatal accident."