bbc.co.uk
Brown signals support for Trident
Trident will be decommissioned by about 2024
Gordon Brown is expected to signal that he wants to keep and renew Britain's independent nuclear deterrent.
The Trident missile system and the Vanguard submarines that carry them need replacing by 2024 and a decision is set to be taken in the next year.
Mr Brown is expected to use his Mansion House speech to indicate his personal commitment to renewing Trident.
Estimates of the cost vary from £10bn to £25bn, depending on what form the new missiles or submarines take.
As well as voicing fears over the cost, critics say Trident is outdated, designed to deal with the threat posed by the Soviet Union during the Cold War, and should now be stood down.
Labour had a manifesto commitment to retain an independent nuclear deterrent but it only applies until the next general election.
Mr Brown, seen as the most likely next prime minister, will speak of retaining the deterrent in the long term.
It is thought he wants anti-nuclear campaigners to know that he is just as committed to replacing Trident as Tony Blair.
'No moral reason'
BBC political editor Nick Robinson said Mr Brown's words would take the heat off the prime minister, who could have produced "uproar" if he had made the same announcement.
The government's position is that decisions on updating or replacing Trident are likely to be needed during the current Parliament.
A Ministry of Defence spokesman said: "No decisions have been taken on the replacement of Trident, either in principle or detail."
When we face nuclear threat, to decide on a new Trident replacement is beginning a new nuclear arms race
Kate Hudson
Chairwoman, CND
But the decision is expected to be taken in months rather than years.
Kate Hudson, chairwoman of the Campaign for Nuclear Disarmament, said she feared Mr Brown's words would close down the debate on Trident promised by the government.
"We were hoping that any potential future prime minister would stick by the commitments made last year by then Defence Secretary John Reid for a full public and parliamentary debate," she told BBC News.
"Our feeling is statements like this from someone as significant as Gordon Brown pre-empts that debate."
Statesman's spin?
Ms Hudson said this was the moment to start multi-lateral disarmament talks.
"At this point, when we face no nuclear threat, to decide on a new Trident replacement is beginning a new nuclear arms race," she said.
Labour MP Ian Gibson, an opponent of Trident, said many young Labour backbenchers had been weaned on CND and had not lost those early political views.
"So it may not be as easy [to agree to replace Trident] as people might think because the chancellor says so," he told BBC News 24.
The Conservatives accused Mr Brown of "spin" designed to make him look statesmanlike.
Shadow defence secretary Liam Fox said: "His words are exactly the same as those in the 2005 manifesto and are not new.
"The chancellor is reheating an old pledge to retain the current nuclear deterrent but he is not committing to replacing the independent nuclear deterrent when it reaches the end of its current life."
'Squandered'
The Tories highlighted that in 1984 Mr Brown had called Trident "unacceptably expensive, economically wasteful, and militarily unsound".
Liberal Democrat defence spokesman Nick Harvey said the British people deserved plans for a scheme that could cost £25bn to undergo full scrutiny.
"Gordon Brown's posturing on Trident is smothering the national debate that this government promised to the British people," he said.
Former Labour Cabinet minister Peter Mandelson said he had not read the speech but added: "I'm sure the speech will spark a very interesting national debate on the subject."
At prime minister's questions on Wednesday, Labour's Gordon Prentice, (Pendle), told MPs it would be an "absolute outrage" if billions were "squandered" on a new generation of nuclear weapons without a vote by MPs.
Mr Blair replied: "There should be the fullest possible debate on this issue. I am sure there will be."
He might well retain Trident but i bet he will cut the number of subs and missiles per sub to an absolute minimum.....
Oh, that's been done with pretty much all of the Navy already 