Prime Minister Tony Blair considered quitting this year because the "considerations of his family became very pressing", Labour peer Melvyn Bragg said yesterday.

Lord Bragg told the ITV News channel that the Prime Minister was under "colossal strain".

Interviewer Alastair Stewart asked the novelist and arts TV presenter - whose wife Cate has co-authored a book about No 10 spouses with Cherie Blair - whether Mr Blair had really considered resigning.

Lord Bragg replied: "I think that he was under tremendous stress. He was being hammered in the Press.

"Perhaps he had doubts about some policies, perhaps not. But in my view, the real stress was personal and family, which matters most to him.

"And my guess is that the considerations of his family became very pressing and that was what made him think things over very carefully. That is my guess.

"What people don't seem to get is how very, very strong he is. And how very determined he is to help make this country a better place, as is Gordon Brown. And he thinks he is on track to do that.

"But yes I think he was under colossal strain, you could see it.

"And my guess was that it was domestic rather than anything else.

"Domestic not in any sense about him and Cherie - I have never seen a couple get on as good as those two. It is not that."

Lord Bragg added: "I call myself a friend, and I'm certainly a supporter of the Labour Party first of all, but I'm no expert on the private life of Tony Blair."

Lord Bragg's comments are the latest in a series of reports that Mr Blair considered resigning earlier this year.

And, ironically, they came a week after the Prime Minister persuaded Darlington MP Alan Milburn to return to the Cabinet. Mr Milburn quit last year to spend more time with his family.

Mr Blair's official spokes-man said 10 Downing Street had no idea Lord Bragg was about to comment publicly about Mr Blair and his family.

"I must admit it took us by surprise," he said. "I don't know why he said it. What Lord Bragg said is a matter for Lord Bragg."

On the question of whether Mr Blair had considered quitting, the spokesman said he had "nothing to add" to the Prime Minister's comment in a July press conference, when he was asked if he had ever thought about moving on during his ten years as leader. Mr Blair responded: "No."

The spokesman refused to discuss how close Lord Bragg was to Mr Blair, saying: "I'm not going to comment on the friendships or otherwise of the Prime Minister."

In the past, Mr Blair has said the "biggest worry" he has in running the country is protecting his four children - Euan, 20, Nicky, 18, Kathryn, 16, and Leo, four - from the limelight.

"The hardest thing about this job is making sure your children grow up normally - and they are, with the odd little mishap, as people know," he said, referring to Euan's arrest at the age of 16 for being drunk and disorderly.

"I am desperate to keep it that way. It is the biggest worry that I have about doing the job."