Tony Blair is to remain Prime Minister for "several years" - and party figures should stop undermining him, Defence Secretary John Reid said last night.

In an interview with The Birmingham Post, Dr Reid criticised colleagues who have been speculating about who will replace the Prime Minister.

He did not name the people he was criticising. But his comments followed public speculation by a number of Cabinet members about Gordon Brown replacing Tony Blair.

In recent days Culture Secretary Tessa Jowell, Pensions Secretary David Blunkett and Northern Ireland Secretary Peter Hain have all publicly stated that they expect the Chancellor to become the next Labour leader.

But Dr Reid said: "There is several years' work there, and Tony will be here to carry that work through for several years."

Asked about who will replace Mr Blair, he said: "I think we should concentrate on the issues the public are interested in, given that the Prime Minister will be with us for several years.

"When the Prime Minister decides he is going, that is the time for us all to start speculating, and it will be the party that chooses, not a few people like me.

"But I will make my view known then. You don't have to be a genius to work out what happens if you play the press's game.

"What happens is, you start speculating, and then the press says 'ah, most people seem to be for him. So if he is the new leader, why is he (the existing leader) there? Why doesn't he go?'

"So that is why I won't play this game of speculating and undermining the present leader of this party, because I think he is an enormous asset to the party and the country."

He added: "I think Tony Blair is the greatest leader the Labour Party has ever had. He is certainly the most successful. No other party leader has ever had three successive victories with a working majority. He has led the most popular party in Britain's political history for the longest period in the opinion polls, since they began.

"And more importantly, he has saved two million jobs, he has presided over a stronger economy, and a fairer Britain than ever before.

"That tells us he is an asset to this party we would do well to retain for as long as we can.

"He has said he will serve a full third term. I am very glad about that, as I think the vast majority of the people in the country are.

"And that is why I will not take part in games about trying to speculate about this and that, thereby undermining the Prime Minister."

Dr Reid also told The Birmingham Post he believed Labour should be the party of the middle classes and proud of it, as well as the party of working class people.

"Middle class people are just working class people who have done well," he said.