By RICHARD KAY and MICHAEL SEAMARK, Daily Mail

Last updated at 09:57 20 May 2006

One of David Cameron's 'A-list' Parliamentary candidates had a secret affair with a key member of the Shadow Cabinet, the Daily Mail can reveal.

Liz Truss had an 18-month relationship with married front bencher Mark Field, the Tories' 41-year-old culture spokesman.

Yesterday, as she pushed a pram carrying her two-month-old baby, 30-year-old Miss Truss refused to comment on the affair, which ended last June.

But Mr Field has told friends that the liaison with the married Miss Truss has cost him his own marriage. He and his wife are divorcing.

It is a huge embarrassment for Mr Cameron, who considers Mr Field to be a high-flying member of the team he wants to take into government.

Equally damaging is the fact that the ambitious Miss Truss is on the list of 100 preferred candidates the Tory leader plans to impose in safe seats.

She has been strongly tipped to inherit the rock solid Bromley and Chislehurst seat in Kent that has become available after the death of maverick Right-wing MP Eric Forth.

Miss Truss stood for Labour-held Calder Valley in last year's General Election, narrowly missing out on getting to Westminster.

It is understood she and Mr Field, who is MP for Cities of London and Westminster, were conducting their affair during the 2005 election campaign.

According to friends, their relationship began at the start of 2004 when Miss Truss, a party activist, was sent to work for Mr Field, who was then the Tory spokesman on London.

Mr Field told one friend: "These things happen and of course it was a bit of a risk. But then these things always are a bit of a mess."

All over

Mr Field, the Oxford-educated son of an Army major, claims the physical relationship ended last June. Some weeks later Miss Truss, who lives in South-East London with her husband, Hugh O'Leary, 32, told the politician she was pregnant. Her baby was born on March 18 this year.

Miss Truss refuses to discuss her relationship with Mr Field but has told friends that her husband is the father of the baby. It is understood that the former lovers are no longer friendly.

Mr Field's wife Michele, who is chief executive of the UCL Hospitals Charitable Foundation, is citing her husband's adultery with Miss Truss in their divorce. She learned of his infidelity only last autumn, some months after her husband and Miss Truss had stopped seeing one another.

A close friend of Mr Field said: "It was a very sad situation. There were a lot of tears but Mark told her absolutely everything and this development will not come as a surprise to her.

"But the marriage had been in trouble for some time and the couple had been drifting apart anyway at the time of his affair."

Mr Field, a former solicitor who set up a publishing and recruitment business in the City before entering Parliament, inherited one of the most prestigious seats in the country in 2001 from former Ulster Secretary Peter Brooke.

The Fields, who have been married for 12 years, have no children and live in a Belgravia townhouse which is now on the market. The couple still share the marital home and until recently continued to attend constituency events together. At Christmas they sent out joint cards and their answerphone still carries a message from "Mark and Michele".

On the rocks

The first signs that the marriage was on the rocks emerged in March when Mr Field attended a banquet at Lon-don's Guildhall for the Brazilian president without his wife. It is understood he told his constituency association of their separation - but not the reason for it - earlier this year.

According to friends, Mr Field and Miss Truss stopped their affair last June but continued to see each other "as friends" for three months. It is understood Miss Truss told Mr Field she was pregnant when they last met in September.

A senior Conservative revealed: "The Tories have a system of established MPs acting as mentors to young activists. Liz, who very much wants to be an MP, was sent to 'shadow' Mark in his role but it seems Mark took his mentoring duties more seriously than intended."

Miss Truss grew up in Leeds and attended a comprehensive before winning a place at Oxford. The daughter of a university professor, she held senior positions in the oil and telecommunications industry before becoming a director of Cable and Wireless.

Last night Mr Field declined to comment on the affair but said: "This is a private matter. My wife and I announced our separation at the beginning of the year and we are now divorcing." Miss Truss's husband said at their £380,000 two-bedroomed Victorian terrace house in Greenwich: "I don't want to talk."