Gordon Brown's chances of becoming Labour leader without any real opposition looked increasingly likely tonight after potential rival Alan Johnson, the Education Secretary, joined the race to become his deputy.

Mr Johnson said he will not challenge the Chancellor for the top job and will instead concentrate on his desire to replace John Prescott as deputy leader.

"I made it clear - in fact I think I said before anyone else - that my interest was in the deputy leadership. That’s the job I want to focus on. I think it’s an important job. I think it’s crucial to have a leader/deputy leader team," said Mr Johnson

He had been touted as an "anyone but Gordon" candidate who would prevent Mr Brown's coronation as Labour leader when Mr Blair steps down next year.

But today the education secretary endorsed Mr Brown's leadership credentials, telling the BBC: "I think actually there is a feeling throughout the party that Gordon is a towering political figure.

"It is, of course, a matter for the party to decide who the leader going to be, but my view is that Gordon is a towering political figure. It is not a position I ever sought and there is a superb candidate in Gordon Brown."

Asked why he had decided not to challenge Mr Brown for the leader’s job, he said: "I don’t want to go for the position.

"You have to first of all decide whether you want to do it. Secondly, you have to decide whether - if you want to do it - is there someone much better for the job.

"On the first question, I didn’t want to do it, and on the second question, there is someone vastly superior."

So far left-winger John McDonnell is the only MP to declare himself as a leadership contender and some reports suggest that Mr Johnson and John Reid, the Home Secretary, would struggle to get the support of the 44 MPs needed to challenge Mr Brown.

Michael Meacher, the former environment minister, today refused to rule himself out as a centre-left candidate to replace Mr Blair, saying discussions on whether he would stand would "come later".

In spite of claims from Mr Brown and others that they would prefer a contest to a coronation, it now seems unlikely that the Chancellor will face opposition from fellow Cabinet members.

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