Image caption The future of Britain's Trident nuclear programme has split the coalition

The Liberal Democrats are considering calling for Britain to give up its permanent at-sea nuclear deterrent within the next few years.

They are expected to use a review of Trident to say some of the UK's four nuclear submarines should not be replaced after they are decommissioned.

But senior figures are now pushing to end Britain's continuous at-sea deterrent even earlier, from 2016.

A decision about the future of Trident has to be made by that point.

This would mean that some of the existing Vanguard submarines would be confined to port with skeleton crews and used for spare parts to keep the remaining boats operational.

The hope among Lib Dems is that this would not just save billions of pounds but would also send a signal that it is possible for a nuclear state to reduce its arsenal while keeping some kind of a deterrent.

'Kept in port'

This was hinted at last week when Lib Dem Treasury chief secretary Danny Alexander said it was time "to move on from the Cold War postures of the past" with a credible deterrent that "can play a role in supporting disarmament in future".

One senior Lib Dem MP said: "We are looking at ending continuous at-sea deterrent even earlier. We don't have to wait until the subs need replacing. We could just keep them in port now."

Another Lib Dem MP said: "If you thought that you could sustain a meaningful deterrent with two boats, then nothing would prevent you using the existing boats on the same principle.

"It would be reckless to scrap them but you could cannibalise them for parts.

The proposal is contained in an internal party policy paper on defence which is said to be at a "pretty late stage of development" and will be put to the Lib Dem conference in September.

Mr Alexander has chaired the government's review of Trident which is sitting on David Cameron's and Nick Clegg's desks and will be published shortly.

It is expected to say that some of the potential alternative ways of delivering nuclear weapons - from land or from air - are either too expensive or too impractical. But the review is expected to consider the option of scaling back the current submarine-launched system.

Most military experts agree that it would be impossible to provide a continuous, around-the-clock nuclear deterrent with less than four Vanguard submarines. With training and repairs, there is frequently only one submarine on duty at sea.

'Credible'

The Conservatives are committed to a like-for-like replacement of Trident which is estimated to cost as much as £20bn. But many Lib Dems believe that Trident is too expensive and distorts the defence budget.

They hope to argue that it would be better to spend the money on troops and kit.

Last week Mr Alexander told the BBC's Andrew Marr programme that the review was seeking to answer whether like-for-like replacement was "the only way to protect our country in future".

"And while the review doesn't come to any conclusions, I think when we publish the results in a few weeks time people will see that there are choices available to this country, there are alternatives where we can move on from the Cold War postures of the past and try and set out a new future for this country with a deterrent that is credible but where this country can play a role in supporting disarmament in future."

A Lib Dem spokesman said: "The Cabinet Office-led review into alternatives to Trident has now been submitted to the prime minister and deputy prime minister.

"The review's findings will now be considered and an unclassified version will be published in due course."

A senior Conservative source said: "Abandoning our continuous at sea deterrence, which has been the ultimate safeguard of our national security for more than 45 years, would be a reckless gamble.

"And leaving our nuclear-armed submarines rusting in port, and then seeking to deploy them at a time of crisis would not only put Britain's security at risk, but would also risk escalating global tensions.

"Conservative policy is clear: we will safeguard Britain's national security and maintain our continuous at sea deterrent."

John Woodcock, Labour MP for Barrow and Furness, said: "Unilaterally ending the commitment to keeping at least one nuclear submarine operational at all times will make no meaningful contribution to global non-proliferation, in fact it could have the opposite result by unsettling other countries who are currently under NATO's umbrella of protection.

"The Liberal Democrats are finally admitting there is no alternative mini-deterrent that could save billions, but few will be taken in by their latest fallacy that a part-time deterrent could save lots of money and protect Britain adequately in the event of a threat in future decades."