The night John told Pauline he'd been having an affair

The former deputy prime minister kissed, and now his wife is telling. Her candid new book reveals all

Pauline Prescott, the wife of the former deputy prime minister, has told for the first time of the night he confessed to an affair with his secretary, shaking to the foundations what had been regarded as one of the most enduring marriages in British politics.

Mrs Prescott initially thought her husband of 45 years was joking when he arrived home in Hull from a conference in Barcelona in April 2006 and suggested they go straight to the bedroom. But, "with a face like granite", he told her he had had a two-year liaison with Tracey Temple, his diary secretary and a friend of Mrs Prescott.

In her autobiography, Smile Though Your Heart is Breaking, published next month and being serialised by the Mail on Sunday, Mrs Prescott gives a raw account of his confession.

"I sat on the dressing-table stool. 'You look so serious,' I said, still half laughing. 'You don't want a divorce, do you?' 'No,' he said. 'But you might once you've heard what I've got to say.' My heart did a flip.

"'I've had an affair,' he said. No. Not my John. Not the man whose life and bed I'd shared for the last 45 years. Not the boy who once saw his father kissing another woman and was so affronted he went to the police station to report him. Not the John I thought I knew; this bright, impassioned man of the highest principles.

"'Were you in love with her?' My heart was thumping against my ribcage. 'No!' he shook his head vehemently. 'There were no feelings involved at all. It ended a while ago – she finished it.' I knew he was being honest then."

She threw him out of the house and tells how, as the media gathered on her doorstep the next day, she focused on some building work. "Strange as it sounds, the installation of my new loo became my salvation," she wrote.

The fling had begun at the Deputy Prime Minister's office party in 2002 and continued during meetings at the then 67-year-old politician's grace-and-favour Whitehall flat.

When exposed by the press four years later, Mr Prescott said: "I did have a relationship with [Tracey Temple], which I regret. I have discussed this fully with my wife, Pauline, who is devastated by the news." The couple had married in 1961, when Mr Prescott was a 23-year-old steward with the Cunard line and his bride a 21-year-old hairdresser.

Mrs Prescott recounts her surprise at receiving supportive phone calls from Cherie Blair, Alastair Campbell and Harriet Harman, then the dawning realisation that her decision on whether to take him back would have a massive impact on the government.

"They'd only just survived the scandal of Home Secretary David Blunkett's affair with a married American journalist. They didn't need another."

Mrs Prescott also reveals that at their first meeting after she kicked him out, she persuaded him not to leave his job, calling it "a coward's way out".

"He told me he planned to resign as Deputy Prime Minister. I knew there had been many calls for him to do so since news of the affair broke, but I wouldn't hear of it," she wrote. "'Oh no you don't,' I said, furiously. 'You've worked too hard for this. We all have. There's an election coming and you must finish what you started."

Mrs Prescott goes on to detail how they repaired their marriage: "People have asked me if I have forgiven him and the answer is that I haven't... [But] I felt John deserved a second chance. He has been a diligent worker, a devoted Labour Party member, a loving husband and a terrific father to our two boys. It wouldn't have been fair to have thrown all that away out of revenge."