MP - I almost threw away my marriage

The South Staffordshire MP said that while working for a fireplace manufacturing firm in Yorkshire in 2004 he engaged in a 'flirtatious' relationship with a co-worker, confessing they shared a kiss a 'couple of times'.

He said admitting the infidelity to his wife Joanne had been one of the most difficult conversations of his life, but said she had forgiven him.

He said: "'My family means everything to me and I almost threw it away."

He added: "I had a good relationship with everyone I worked with, but with one person this started to develop into something more.

"We had to travel together and spent a lot of time in each other's company, the relationship became flirtatious and a couple of times we shared a kiss.

"It never went further than that, but this had a profound impact on us both and those close to us. It was a dreadful mistake and stopped as suddenly as it had started."

Mr Williamson is understood to have revealed details to party officials before running for selection as an MP and has informed Downing Street.

He took over as Defence Secretary in November after Sir Michael Fallon's resignation amid sleaze allegations.

Sir Michael became engulfed in the Westminster sex harassment scandal when a journalist told Downing Street he had attempted to kiss her during a lunch meeting.

Mr Williamson then became the youngest Defence Secretary since the role was created during the Second World War, leap-frogging more experienced ministers to take the role in November.

The 41-year-old MP served as parliamentary private secretary to David Cameron from 2013-16.

He was selected by Theresa May as her parliamentary campaign manager for the Conservative leadership contest triggered by Mr Cameron's resignation.

The former Chief Whip achieved the highly unusual distinction of being promoted directly into the Cabinet without having held a more junior ministerial job.