The UK's nuclear weapon system on the Clyde could be downgraded to a "part-time" deterrent, a long-awaited report is expected to suggest today.

Ministers are to publish the results of a high-level review of alternatives to a like-for-like replacement for the ageing Trident.

The analysis was a key concession to the Liberal Democrats when they entered into Coalition government with the Conservatives in 2010.

Party leader Nick Clegg has said that it would be wrong to spend large amounts of money replacing a Cold War system designed to "flatten Moscow".

No 10 made it clear yesterday that the Prime Minister had "seen no evidence" of a viable alternative to Trident.

Defence Secretary Philip Hammond also warned it would be "reckless" to downgrade the UK's nuclear deterrent.

David Cameron has long insisted that his party is committed to a full replacement of Trident.

Senior LibDem sources say that they hope that to win over the Labour party by showing them there are credible alternatives to spending £20 billion on a like-for-like system.

A final decision does not have to be made until 2016, meaning that a way forward on Trident is expected to be included in all the main parties manifestoes for the 2015 general election.

The outcomes of the report will be laid out by Danny Alexander the LibDem chief secretary to the Treasury.

He is expected to say that options include cutting the current number of nuclear submarines from four to two or possibly three.

The move would mean ending the deterrent's ability to be "continuously at sea".

The SNP said that "scrapping Trident is the only sensible, logical solution".