NORTH Wiltshire MP James Gray has left his wife but says he will not be quitting his parliamentary seat.

He has admitted to having an affair while his wife Sarah fought breast cancer in the run-up to last year's election.

The Tory MP says he approached senior party members last week and told them of the affair.

In Swindon yesterday, Conservative Party shadow cabinet member Oliver Letwin rejected suggestions that Mr Gray should resign.

He said Tory bosses had known about it for some time. "It's a totally private matter," said Mr Letwin.

"I have been aware of it for some weeks."

Mr Gray, 52, says his marriage is over as a result of his 19-month relationship with countryside campaigner and mother-of-three Philippa Mayo.

He told his wife about the relationship three weeks ago.

The couple have been married for 26 years and have three children, John, Olivia and William. He has been MP for North Wiltshire since 1997.

"I deeply regret the pain and suffering I have caused my family and the disappointment it may have brought to my constituents," said Mr Gray.

"I hope that they will give us time and space to plan our futures."

He said he hoped to marry Mrs Mayo, 44, who is moving to North Wiltshire.

"I am not proud of myself but I hope that now we can plan our futures," he said.

A close friend of Mrs Gray, who is away on holiday, said she had had no inkling of the affair.

Mrs Mayo, a Countryside Alliance pro-hunt campaigner, met Mr Gray in February 2005 and they began seeing each other shortly afterwards.

Mrs Gray, 51, was diagnosed with cancer in April 2005.

According to reports, Mrs Mayo's husband Rupert, a London barrister, became suspicious that she was seeing Mr Gray last Christmas and some weeks later confronted her. She admitted the affair but said it was over.

His suspicions continued, however, and early this summer he confronted her again.

She admitted the affair had continued and Mr Mayo moved out of their home in Leicestershire. Their children are aged 14, 12 and nine.

Mr Mayo is said to be heartbroken and has written to Mr Gray, telling him he is not fit for office.

Mr Gray has told the North Wiltshire Conservative Association of his marriage break-up and they are believed to be standing by him.

The local Conservative Party branch is standing behind Mr Gray as their MP.

Wootton Bassett Conservative Branch vice-chairman Chris Wannell said he supported Mr Gray remaining in the North Wiltshire seat.

"Mr Gray is a very good constituency MP," Mr Wannell said.

"It's his private life. I have known James for a very long time and I feel very sad for both of them."