People "overestimated" Gordon Brown's capacity to be prime minister, Tony Blair has claimed.

Mr Blair said the pair's relationship had been "hard, going on impossible" at times and claimed Mr Brown had "backed away" from New Labour principles which could have possibly secured an election win in May.

Blair said he knew Labour would be "in trouble" if the party deviated from the reforming agenda he had set out.

The comments follow criticism for the "difficult, at times maddening" Mr Brown in Mr Blair's memoirs, A Journey.

But he said that people may have "underestimated" the strengths that his successor displayed during his three years in No 10.

Mr Blair said: "The relationship with Gordon was very, very difficult, it was also very close.

Even though, towards the end, frankly it was hard, going on impossible, for a large part of the time we were in government he was an immense source of strength, his contribution to the successes of the Labour government was clear."

Turning to his successor's term in office, Mr Blair said: "I always knew that if we departed a millimetre from New Labour we were going to be in trouble.

"In my view what we needed to do in 2007 was we needed to renew New Labour with vigour, take it to the next stage, being the party that reforms welfare and public services, carried on deepening those reforms. I think we somewhat backed away on them."

"The difficulty is when he was my number two, in a sense, as chancellor to my prime minister, people maybe overestimated his capacity to be prime minister.

"I think in the last three years when he was prime minister people maybe underestimated his strengths."