The plans include a new generation of nuclear submarines at a cost of up to 20 billion pounds (39.5 billion dollars).

In an apparent concession to critics from within his own party and the anti-nuclear lobby, Blair promised to cut the number of stockpiled nuclear warheads by 20 percent from about 200 currently to 160.

But he said: "The government's judgment, on balance, is that though the Cold War is over, we cannot be certain in the decades ahead that a major nuclear threat to our strategic interest will not emerge."

The premier, outlining the government's proposals to retain the US-built Trident missile system to parliament, said there were "new and potentially hazardous" threats from states like North Korea and Iran.

There was no guarantee that "there is a possible connection between some of those states and international terrorism" and that no other nuclear state in the world was considering unilaterally getting rid of its capability, he said.

"In these circumstances, it would be unwise and dangerous for Britain, alone of any of the nuclear powers, to give up its independent nuclear deterrent," he told the lower House of Commons.

Blair argued that action was needed immediately to take the first steps towards maintaining Trident, because of the estimated 17 years it takes to design build and deploy a new submarine.

A new generation of submarines would cost between 15 billion pounds and 20 billion pounds (22.2 billion-29.7 billion euros, 29.6 billion-39.5 billion dollars), including design and manufacturing costs, he added.

No decisions were needed on the warheads, as the lifespan of the Trident D5 missile can be extended to 2042, he said.

Blair rejected concerns that by retaining Trident, Britain was in breach of its obligations to nuclear non-proliferation.

"We have the smallest stockpile of nuclear warheads amongst the recognised nuclear weapons states, and are the only one to have reduced our stockpile of operationally available warheads to no more than 160, which represents a further 20 percent," he said.

"Compared with previous plans, we will have reduced the number of such weapons by nearly half."

The issue of replacing Trident is likely to dominate the political agenda in the coming months before a parliamentary vote on the matter in March.

Nuclear weapons are a divisive issue within Blair's governing Labour Party, as unilateral disarmament was a key plank of its policy at the height of the Cold War during the 1980s.

But he is unlikely to suffer an embarrassing defeat in parliament.

The leader of the main opposition Conservative Party, David Cameron, told Blair his party agreed with Blair's position "on substance and on timing".

Opponents, including the anti-nuclear lobby have claimed that Blair is trying to rush through a decision without a proper public debate and under pressure from the defence industry.

They also pointed to the cost of replacing the system, with observers putting estimates on anything from 25 billion pounds upwards.

The Trident system is currently based on four Vanguard class Royal Navy submarines, one of which is always on patrol and fully armed.

Mr. Blair was speaking in Parliament to present a policy document, known as a White Paper, expected to be debated at some length before a vote next March. At present, Britain is one of the five permanent members of the United Nations Security Council who belong to the nuclear club, along with the United States, Russia, China and France.

While other nations with nuclear weapons include India and Pakistan, Western leaders like the United States and Britain accuse Iran of seeking such weapons capability. Teheran denies the allegation, saying it is developing nuclear energy for peaceful uses like medical treatments. North Korea conducted a nuclear test last October. Israel has not commented on widespread assumptions that it has a nuclear weapons capability.

Mr. Blair said Britain's only nuclear deterrent consisted of four Vanguard nuclear-powered submarines, equipped with Trident D-5 missiles manufactured in the United States. The vessels will begin to go out of service in 2022, Mr. Blair said, while designing and building replacements will take an estimated 17 years.

Nuclear weapons are a sensitive issue in the governing Labor Party since many of the party's supporters - including, at one time, Mr. Blair himself - have traditionally opposed such weapons. Indeed, until the late 1980's, the party was formally committed to unilateral nuclear disarmament.

But Mr. Blair's supporters are calculating that they can muster sufficient parliamentary support from the opposition Conservatives to squash Labor opposition in next year's vote. As a sop to Labor dissent, however, Mr. Blair said today that Britain would consider reducing its submarine force from 4 to 3 and might cut its "stockpile of operationally available warheads" by one- fifth to "no more than 160."

He insisted, though, that Britain should not dispense with the nuclear capability.

"The risk of giving up something that has been one of the mainstays of our security since the war, and moreover doing so when the one certain thing about our world today is its uncertainty is not a risk I feel we can responsibly take," Mr. Blair said in Parliament. "Our independent nuclear deterrent is the ultimate insurance."

Apart from other arguments, he said, "the new dimension is undoubtedly the desire by states, highly dubious in their intentions, like North Korea and Iran, to pursue nuclear weapons capability."

He continued: "The notion of unstable, usually deeply repressive and anti-democratic states, in some cases profoundly inimical to our way of life, having a nuclear capability is a distinct and novel reason for Britain not to give up its capacity to deter."

"It is not utterly fanciful either," Mr. Blair added, "to imagine states sponsoring nuclear terrorism from their soil. We know this global terrorism seeks chemical, biological and nuclear devices. It is not impossible to contemplate a rogue government helping such an acquisition."

Some opponents of nuclear weapons said Britain should spend its money on the environment, not on weapons. But labor unions representing shipyard and engineering workers said thousands of skilled jobs would be secured by a new nuclear submarine program.

"He talked vaguely about reducing the number of submarines and warheads but it is not clear what that would mean. I am sure many Labour MPs will be extremely angry because it is clear the Prime Minister has set out a pre-determined timetable," she said.

Bob Crow, general secretary of the Rail Maritime and Transport union, said: "We need to spend money on saving the planet, not on weapons that can help destroy it.

"The £25 billion the Government wants to spend on replacing Trident - and it could be three times that - could go a long way to helping Britain reduce carbon emissions, build some of the transport infrastructure we desperately need and to help bolster our public services.

"Blair took us into an illegal war over weapons of mass destruction that didn't even exist, and now he wants to tear up the nuclear non-proliferation treaty to build some new ones of his own - there is only one word for that, and it is hypocrisy.

"While there is starvation, poverty, homelessness, illiteracy and a grave environmental threat hanging over our planet it would be nothing short of obscene to go ahead with replacing Trident, whether it's with 200 warheads, 100 or just one."

Keith Hazlewood, national officer of the GMB union, said there were many practical issues which had to be debated in the coming weeks, insisting: "Unless new orders are placed soon the skills and technical expertise needed to do this submarine building will be lost to the UK.

"If this happens the UK would struggle to build these vessels if they were to be needed in the future.

"If Parliament decides not to go ahead it must pay heed to the impact on jobs and on communities that will be affected as well as the impact on UK manufacturing as whole."

The Prime Minister presented a White Paper approved by the Cabinet this morning that recommends the replacement of Britain's fleet of four nuclear-armed submarines when they come to the end of their service in 2024.

Mr Blair said that a new nuclear fleet would take 17 years to design, build and test so a decision would have to be taken next year.

He said that the final cost of the submarines would be between £15 and £20 billion and consume 3 per cent of the defence budget over the coming three decades.

The life of Britain's D5 Trident nuclear missiles, which are also used by the US, can be extended until 2042, the Prime Minister said, so no decision was needed on their future was needed now.

But he added that he would be writing to President Bush to seek American collaboration in developing the next generation of missiles.

In a concession to Labour backbenchers who oppose Britain's nuclear capabilities, he said that the fleet might only need three submarines, but that a final decision would depend on their design. Two submarines would not be enough to ensure that one is at sea at all times.

In another offer to rebel MPs, Mr Blair said the plan also envisaged a 20 per cent reduction in the UK's stockpile of nuclear warheads: from 200 to 160.

"Ultimately, this decision is a judgment, a judgment about possible risks to our country and its security; and the place of the deterrent in thwarting those risks," he told the House Commons.

"The Government's judgment, on balance, is that though the Cold War is over, we cannot be certain in the decades ahead that a major nuclear threat to our strategic interests will not emerge."

Mr Blair said that the nuclear ambitions of countries such as North Korea and Iran and the potential connections between those regimes and international terrorism meant that it would "be unwise and dangerous for Britain, alone of any of the nuclear powers, to give up its independent nuclear deterrent".

He criticised as naive the thought that Britain could persuade other countries to disarm by abandoning its nuclear programme. "More likely, they would construe it as weakness," he said.

But he acknowledged the opposition that the Government is likely to incur in its commitment to the nuclear deterrent.

"There are perfectly respectable arguments against the judgment we have made. I both understand them and appreciate their force," he said.

"It is just that, in the final analysis, the risk of giving up something that has been one of the mainstays of our security since the War, and moreover doing so when the one certain thing about our world today is its uncertainty, is not a risk I feel we can responsibly take.

"Our independent nuclear deterrent is the ultimate insurance."

The Conservatives, on whose votes Labour may have to rely to approve the plan, offered their immediate support for a new nuclear fleet.

David Cameron said he agreed with the Government's White Paper "on substance and on timing" but urged that a decision on whether a fourth submarine is needed not be taken until 2020.

The replacement of the Trident fleet is expected to safeguard more than 15,000 jobs in Britain's defence and shipbuilding industries and was welcomed today by arms manufacturers and the submarine-building yard at Barrow, in Cumbria.

But it has already aroused significant criticism from anti-nuclear campaigners, a former Defence Minister and the Anglican church. This summer, 19 bishops and the Archishop of Canterbury described Britain's weapons of mass destruction as "evil".

This morning the Campaign for Nuclear Disarmament (CND), supported by a clutch of Labour backbenchers, launched an "Alternative White Paper", saying that nuclear weapons offered no deterrent against terrorism and that Britain should take the lead in multi-lateral nuclear disarmament by letting its nuclear programme expire in 2024.

Labour rebels also spoke out against the short period of consultation before the House of Commons votes on the proposal - just three months - and the Government's intention to "whip" the vote on what should be a matter of conscience.

"If the government is really serious about taking into account the views of its own backbenchers and others, then they would extend the consultation timetable and also allow a free vote," said Linda Riordan, Labour MP for Halifax. "I suspect though, they have already made up their minds."

Michael Meacher, Labour MP for Oldham West and Royton, said: "If greater security is the defining factor, then the UK absolutely should not replace Trident. It answers no threats that we currently face and in fact creates more."

Relevant links from Nuclear Information Service:

PM outlines plans for nuclear deterrent
Read the full transcript of the statement

The PM said that "from today there would be a very full process of debate and at the conclusion of that process in March next year they intended to have a vote in the House of Commons."

The White Paper on the nuclear deterrent is published today.
Read the White Paper
 

See HMS Vanguard launch a missile, wmv 2.82MB
More on Britain's nuclear deterrent
Read about life on a nuclear submarine
 

10 Downing Street Press Release - 4 December 2006

The Prime Minister has made a statement to the House of Commons about the Government's decision to maintain the United Kingdom's independent nuclear power deterrent, saying that "maintaining our nuclear deterrent capability is ... fully consistent with all our international obligations."

Tony Blair said that there were "many complex technical, financial and military issues to be debated in respect of this decision," adding that "none of them obscured or altered the fundamental political judgment at the crux of it. Britain has had an independent nuclear deterrent for the last half century."

He went on to say that "the whole point about the deterrent is not to create circumstances in which it can be used but on the contrary to create circumstances in which it is never used - to thwart risks to the United Kingdom and its security.

The Prime Minister said the the decision to replace the UK's current Trident missile system had to happen now is because the current nuclear capable submarines will potentially reach the end of operational service from the early 2020s. It is estimated that it would take 17 years to introduce into service any submarine-based replacement, meaning that the initial steps would have to take place in 2007.