Called a “great American hero” by his family, Mr Felt, 91, the FBI’s deputy director during the early 1970s, received a blast of vitriol from old Nixon hands for his role in leaking information to The Washington Post and helping to bring down the President.

While most of Washington marvelled that one of the great modern political mysteries had finally been solved, central figures in the Watergate scandal, some of whom served prison sentences for their role, denounced Mr Felt.

Pat Buchanan, a former Nixon speechwriter, called him a traitor for being a key source for the Post reporting team of Bob Woodward and Carl Bernstein as they pursued the Watergate conspiracy, which eventually led to Nixon’s resignation in August 1974.

In their book about the Watergate scandal, All the President’s Men, the two reporters describe how Deep Throat met Woodward late at night in underground car parks.

Meetings would be arranged with a classic cloak-and-dagger flourish: Woodward would call one by displaying a flowerpot on his balcony; Deep Throat by penning a clock face on page 20 of Woodward’s copy of The New York Times, which was delivered to his doorstep before 7am.

“I think Mark Felt behaved treacherously,” Mr Buchanan said. “I’m unable to see the nobility of the enterprise, sneaking around in garages, moving pots around, handing over material he got in the course of the investigation.”

Charles Colson, a senior Nixon adviser who served seven months in jail for obstruction of justice, said: “When any President has to worry whether the deputy director of the FBI is sneaking around in dark corridors peddling information in the middle of the night, he’s in trouble.”

Leonard Garment, Nixon’s domestic policy adviser, said: “I don’t think Deep Throat was a hero. Nixon did many good things. I don’t think someone who contributed to his destruction was a hero.”

Mr Felt, after 30 years of silence, admitted to Vanity Fair magazine that he “was the guy they used to call Deep Throat”, after being persuaded to emerge from the shadows by his family.

Even President Bush commented: “It was a revelation that caught me by surprise. A lot of us were wondering for a long time who it was.”

While his family described Mr Felt as a patriot who wanted to protect America from a “horrible injustice”, a picture emerged yesterday of a man who may have acted as much out of thwarted ambition as love of country.

A career FBI man, Mr Felt was furious after being passed over for the bureau’s top job after the death of J. Edgar Hoover, who died a month before the Watergate break-in.

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