Deep Throat began as mentor

Mr Woodward was a navy lieutenant on an assignment when he met former deputy FBI chief Mark Felt in a West Wing waiting room in 1970.

Mr Felt was then working as an assistant director at the FBI and got talking with Mr Woodward, who at the time was tossing up a law career.

“As I think back on this accidental but crucial encounter – one of the most important in my life – I see that my patter probably verged on the adolescent,” Woodward says in a Washington Post article.

“Since he wasn’t saying much about himself, I turned it into a career-counselling session.”

Mr Felt would become Mr Woodward’s mentor and once he finally settled on journalism, a reliable source of insider information.

Mr Woodward says Mr Felt was opposed to Nixon administration and was deeply concerned by the White House’s political manipulation of the FBI.

According the Mr Woodward he “thought the Nixon team were Nazis.”

During the Watergate story the pair devised a clandestine communications system.

Urgent meetings between them would be called through the “flower pot signal” in which a pot plant would be moved on Mr Woodward’s balcony.

Their regular rendezvous was at the basement of an underground car park in Washington DC.

“There was no fallback meeting place or time. If we both didn’t show, there would be no meeting,” he says.

“Felt said if there was something important he could get to my New York Times – how, I never knew.”

“Page 20 would be circled, and the hands of a clock in the lower part of the page would be drawn to indicate the time of the meeting that night, probably 0200, in the same Rosslyn parking garage.”

Mr Felt revealed himself as Deep Throat on Tuesday, 30 years after the Watergate scandal forced President Nixon to resign.