By Rob Watson Defence and security correspondent, BBC News

There is no doubt Chancellor Gordon Brown has set off a major ideological debate within his own, once avowedly, anti-nuclear Labour Party.

But what are the military arguments for and against Britain retaining an independent nuclear deterrent?

Nuclear submarines are based at Faslane on the Clyde

Perhaps the first question to consider is why this is an issue now.

At the moment Britain has 16 Trident missiles, based on four nuclear submarines, providing a total of 200 warheads.

The problem is that the missiles will reach the end of their operational life by the year 2024 and it is argued by some experts that a decision is needed now to allow enough time to replace the system, if indeed Britain is to retain a nuclear weapons capacity.

The arguments against doing so run something like this:

It is said by some critics Britain would not really have an independent nuclear deterrent because it would rely on the US for operating and maintaining any new system, just as it has with Trident.

TRIDENT TIMELINE 1980 Margaret Thatcher commits Britain to having Trident 1993 Trident submarine-based nuclear missile programme comes into use replacing Polaris Late 2006/early 2007 Cabinet decision on replacing Trident expected Around 2010 work on new scheme to replace Trident is expected to begin 2024 Britain's Trident submarines due to be decommissioned Trident factfile

And then there is the cost, estimated at anywhere between �12bn and �25bn, which not surprisingly some would rather see spent on things such as schools and healthcare.

The most pointed military argument against replacing Trident however is that it is hard to see Britain ever using a nuclear weapon independent from the US.

The point being that, while it is conceivable to imagine a confrontation with a nuclear-armed North Korea or Iran for example, it is very hard to imagine Britain having to go it alone without the US.

And what use would nuclear weapons be against the asymmetrical threat posed by international or domestic terrorism?

NUCLEAR BRITAIN October 1952: Britain tests nuclear weapon May 1957: First UK hydrogen bomb detonated 1958 US-UK Mutual Defence Agreement signed allowing the sharing of nuclear technology 1968 British submarine armed with US-built Polaris missiles goes on patrol for the first time November 1968: UK ratifies nuclear non-proliferation treaty 1982 Cruise missiles deployed in UK

But there are also powerful arguments for it.

What many military analysts believe, including Dr Lee Willett of the Royal United Services Institute (RUSI), is that ultimately retaining an independent nuclear weapons system is an insurance policy against the unknown, and a reasonably priced one at that.

With countries like North Korea and Iran presumed to either have or be determined to acquire nuclear weapons and others such as Syria, Egypt and Saudi Arabia nursing such ambitions, Dr Willett argues this is not the time for Britain to be getting out of the nuclear game.

HAVE YOUR SAY We should keep the minimum nuclear arsenal. Whatever the cost Carl Worrall, York Send us your comments

Then there is the political and diplomatic argument - that it is vital for Britain to maintain its big power role in the world, including its permanent seat at the United Nations Security Council and its status within the European Union and with the US.

As to the independence of the deterrent from the US, supporters say though it is true any system would likely be acquired from America, its use, like the existing Trident, would be controlled by Britain.

In many ways these are arguments that have been rehearsed over and over again since nuclear weapons were first invented and proliferated around the world.

Does the possession of a nuclear arsenal deter potential foes from attacking you or is their use so inconceivable as to make them in the end a poor deterrent?