Deputy Prime Minister Nick Clegg has accused the Conservatives of "jumping the gun" on Trident as Defence Secretary Philip Hammond announced an additional £350m to design the future generation of British nuclear-armed submarines.
This investment will sustain 1,200 UK jobs and follows the initial £350m of design work announced earlier this year, the Ministry of Defence (MoD) said.
However, the decision to press ahead with spending on the design for the new submarines has reignited coalition tensions over the replacement for Britain's Trident nuclear deterrent.
The issue divides the Tories and the Liberal Democrats, and as part of their coalition-forming agreement both parties promised to delay the final decision on whether to replace the nuclear deterrent until after the next general election.
The Lib Dems are leading a review into cheaper ways to maintain the nuclear deterrent and also want to see the so-called "Moscow criterion", which recommends Britain retains an arsenal capable of destroying the Russian capital, abandoned.
Mr Clegg dismissed suggestions the additional funding "made clear" the Government's commitment to maintaining the system.
The Lib Dem leader insisted the agreement will not be "undermined or contradicted" and the review into alternatives will continue.
"The idea of a like for like entirely unchanged replacement of Trident is basically saying we will spend billions and billions of pounds on a nuclear missile system designed with the sole strategic purpose of flattening Moscow at the press of a button," he said.
"The final decision on Trident replacement will not be taken until 2016, however much other people may not like it that way."
Mr Hammond detailed the plans on a visit to the home of the UK's nuclear deterrent at Faslane on the River Clyde in Scotland.
"The Government's position on this is very clear. We are committed to maintaining a continuous deterrent, based on the Trident missile," he said.
Mr Hammond said the review would inform the main investment decision, "but in the meantime, we are pressing ahead with the design and development work".
Commenting on the Scottish independence debate, the Cabinet minister reiterated the Government's commitment to keep the naval base in Scotland.
He said: "We are confident that the Scottish people will choose to remain part of the United Kingdom.
"The Faslane complex is the largest employment site in Scotland with over 6,500 jobs underpinning the local economy.
"We have no plans to move the nuclear deterrent from the Clyde. On the contrary, we intend to move the Astute and Trafalgar Class attack submarines to Faslane, creating a further 1,500 jobs.
"The Scottish Government needs to explain how their policy would benefit Scotland's economy and safeguard Scottish jobs."
The announcement follows the successful firing of an unarmed Trident ballistic missile by HMS Vigilant during a test launch in the Atlantic Ocean last week.
HMS Vigilant is one of four Vanguard Class submarines which maintain the UK's nuclear deterrent.
The Vanguard submarines will be replaced from 2028 by the Successor which is currently being designed by British companies.
As a result of Mr Hammond's announcement, BAE Systems will proceed with an additional £315m worth of work.
A further £38m will be carried out by engineering support services company Babcock.
SNP MSP Bill Kidd attacked the move and accused Mr Hammond of using "fantasy figures" relating to the number of jobs dependent on the nuclear weapons system at Faslane.
He said: "For the UK Government to boast about spending hundreds of millions of pounds on weapons of mass destruction - while at the same time implementing brutal welfare cuts and slashing investment in the economy - is obscene.
"More than that, Philip Hammond's weak attack on the Scottish people's choice in the independence referendum continues to use fantasy figures relating to the number of jobs associated with Trident at Faslane.
"His own Ministry's figures obtained through FoI show that there are not thousands of jobs dependent on the nuclear weapons system but 520 - all of which and more will be taken up by Faslane continuing as the main Scottish naval base."