Sergeant is retiring from his role of political editor for ITV's news programmes and will leave the news organisation at the end of the year.

He quit the BBC for ITN in 2000 after 30 years to take over Michael Brunson's role as ITV's leading political reporter.

A widely respected journalist, Sergeant was the only correspondent to secure an interview with former Welsh secretary Ron Davies following his resignation in 1998.

Another of his more notable TV appearances was his unsuccessful attempt to interview Margaret Thatcher during the 1990 Conservative leadership campaign.

BBC man: Sergeant pictured in 1982

Attempting to question the then prime minister on the steps of the British Embassy in Paris, he was captured on film being knocked sideways by Mrs Thatcher's handbag.

But he has been able to make light of his embarrassing moment, which is often referred to during his guest appearances on TV satire quiz show Have I Got News for You.

Before becoming a journalist, Sergeant embarked on a brief stage career, performing alongside Alan Bennett, Michael Palin and John Fortune.

He has recently published his memoirs, entitled Give Me 10 Seconds, and has signed a two-book deal with publishing house PanMacmillion.

Sergeant said: "I've had a marvellous time at ITN, it's been the perfect way to round off 21 years of political reporting.

"What prompted the move is very simple - I have signed a very generous deal with PanMacmillion and I am anxious to settle down soon to a new career.

Michael Buerk and Peter Sissons are leaving the 10 O'Clock News

"It's not exactly retirement and I hope to work often in broadcasting. I have a number of offers in the pipeline."

ITV News editor Nigel Dacre said: "John is a remarkable talent and we will be sorry to see him go. But I am delighted that he decided to spend his last three years in full time broadcast journalism - including his last general election campaign - with ITV News.

"We wish him well for the future."

Sergeant is the latest high-profile TV journalist to announce a change of role, following the decision of BBC presenter Peter Sissons to quit the 10 O'Clock News after 13 years.

Sissons is likely to continue at the BBC, with a position being lined up for him on the corporation's rolling news channel, News 24.

Fellow 10 O'Clock News presenter Michael Buerk is also retiring at the end of the year.