Nick Clegg has accused the defence secretary, Philip Hammond, of "jumping the gun" on Trident as Hammond visited Faslane to announce a further £350m investment to underline his support for a fresh generation of British nuclear-armed submarines.
Liberal Democrats are angered at the way in which Hammond appears to be ruling out any other option but full renewal of the current continuous-at-sea deterrent.
A final decision is due to be by government made in 2016, but the coalition agreement sets out plans for a Lib Dem-led government study, based in the Cabinet Office, into alternatives.
An angry Clegg said: "The coalition agreement is crystal clear: it stands, it will not be changed, it will not be undermined, it will not be contradicted. The decision on the Trident replacement will not be taken until 2016, however much other people may not like it that way.
"And I think in the meantime what we need, as a country, is to have a considered, facts-based debate about what kind of deterrent we need in the future, what kind of deterrent we can afford in the future.
"Let's remember the idea of a like-for-like, entirely unchanged, replacement for Trident is basically saying we will spend billions and billions and billions of pounds on a nuclear missile system, designed for the sole strategic purpose of flattening Moscow at the press of a button.
He added, referring to Hammond: "Having seen the papers this morning, I think some people are jumping the gun on this Trident decision."
Lib Dem officials also asked why Hammond appeared to have closed his mind to cheaper alternatives to Trident before the study, due to be completed next year, had been published.
Hammond said: "The government's position on this is very clear. We are committed to maintaining a continuous deterrent, based on the Trident missile.
"There was a vote in parliament in 2007 where there was an overwhelming majority for replacing the Vanguard submarines when they go out of service [in the 2020s]."
But Liberal Democrats said the terms of reference of the review, agreed by the previous defence secretary Liam Fox, clearly show alternatives to a submarine-based deterrent will be considered.A Liberal Democrat source said: "The Conservatives are clearly wedded to a cold war replacement for Trident. The Liberal Democrats will make the case for an alternative. The Labour party has got to come clean [on] whether it supports Britain building a £100bn replacement." The Liberal Democrats recognise they could be potentially the only party going into the next election proposing some alternative to a fully fledged replacement.
The review is being overseen by the Treasury chief secretary Danny Alexander, and is seen as critical to making a practical and military case for an alternative.
Both Liberal Democrats and Conservatives on Monday expressed disappointment at the decision of the Liberal Democrats to remove defence minister Nick Harvey from the Ministry of Defence, saying he had been central to the review.
The former Conservative defence minister Gerald Howarth said he was astonished by the decision, and Lord Lee, a Liberal Democrat peer, said it would be advisable if Harvey was drafted into the review.
The Hammond announcement was also designed to underline the importance of Faslane submarine base to the Scottish economy, and emphasise the folly of the Scottish Nationalists' opposition to Trident.
Hammond said the submarine base generated about 6,500 jobs in the area and that a Scottish navy as proposed by the SNP would generate fewer.
"By the time we've finished transferring all the submarines to Falsane we'll have generated 8,000 jobs in the area, and frankly a Scottish navy would generate nothing like that number of jobs at Faslane. The Conservative party has always made it absolutely crystal clear that we believe the nuclear deterrent has been a formidable part of our defence armoury, and has helped to secure the peace, and indeed helped to end the cold war. We believe that a successor submarine is necessary; we believe that submarine-based nuclear deterrent is the most effective."
Scottish deputy first minister Nicola Sturgeon attacked the UK government for "dumping" weapons of mass destruction on Scotland, and said there is cross-party support for scrapping the renewal of Trident in the Scottish parliament.
"The vast amount of taxpayers' cash squandered by the UK government on designing the new Trident system during a period of austerity and cuts to services and benefits by the Tory-led coalition is a staggering waste of money," she said.
