Gerry Adams phoned Blair to 'express solidarity' over cash for honours

Jonathan Powell, who was Mr Blair's chief of staff from 1995 to 2007, said the two men became so friendly that the Sinn Fein President even called Mr Blair to "express his solidarity" over the police investigation into cash for honours.

In an interview to publicise a book he has written about the Northern Ireland peace process, Mr Powell said that during the cash-for-honours inquiry in 2006, which raised the prospect of criminal charges for Mr Blair and his aides, Mr Adams engaged in banter about the IRA's terrorist struggle against the British.

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He suggested to Mr Powell that he and Mr Blair should "seek political status" if they were arrested and refuse to recognise the court - a reference to the tactics used by Republican activists during the troubles.

Mr Powell's book, Great Hatred, Little Room, tells the behind-the-scenes story of the peace negotiations.

He admits that the success of the policy of engagement with the IRA's leaders persuaded him that the Government should try to establish dialogue with terror groups such as Al Qaeda and the Taliban.

During the interview, published in The Guardian, Mr Powell, who now has a lucrative job with Morgan Stanley investment bank, revealed details about the intimacy of his bond with Mr Blair - including the fact that his boss gave him his old shirts to wear.

He also gave a fresh insight into the intensity of the Blair-Brown feud by disclosing that Mr Brown had conspicuously snubbed him because of his closeness to Mr Blair by walking past him for more than ten years without ever saying hello.

He would also hear the two men yelling at each other through the door of the Prime Minister's office.

Mr Powell has remained close to his former master since leaving No10.

He said that the famously technophobic Mr Blair had been forced to master a BlackBerry device, and bombards confidants with messages around the clock.

He has been helping Mr Blair to reduce the number of engagements he has taken on since leaving office.

"He'd committed himself to something like 462 days [of engagements over the coming year], because he was saying yes to everything," Mr Powell revealed.

"I've just been trying to unravel it and sort of take it down to 300 days."