MoD under fire over fate of 20 retired nuclear submarines
Each vessel will cost almost £100m to dismantle, with seven still containing nuclear fuel.
The Ministry of Defence has been criticised for a "dismal" failure to dispose of obsolete nuclear-powered submarines.
The MoD has twice as many submarines in storage as it does in service and has not disposed of any of the 20 boats decommissioned since 1980, the National Audit Office (NAO) said.
Six of the vessels are berthed at Rosyth, on the Firth of Forth, while the remaining 14 are at Devonport on the south coast of England.
Seven of the boats have been in storage for longer than they were in service, while nine - all stored at Devonport - still contain irradiated fuel.
According to the NAO, disposal costs will run to £96m for each vessel.
The MoD has put its total future liability for maintaining and disposing of the 20 stored and ten in-service nuclear-powered boats at £7.5bn over the next 120 years, underlining the long-term nature of nuclear waste.
The NAO said the MoD does not have a fully developed plan to dispose of the operational Vanguard and Astute submarines or its future Dreadnought-class boats, which have different types of nuclear reactor
Meg Hillier, chairwoman of the Commons Public Accounts Committee, said: "For more than 20 years the Ministry of Defence has been promising to dismantle its out-of-service nuclear submarines and told my committee last year that it would now address this dismal lack of progress.
"It has still not disposed of any of the 20 submarines decommissioned since 1980 and does not yet know fully how to do it.
"The disposal programmes have been beset by lengthy delays and spiralling costs, with taxpayers footing the bill.
"The ministry needs to get a grip urgently before we run out of space to store and maintain submarines and we damage our reputation as a responsible nuclear power."
The vessels being stored at Rosyth include the first submarines used to carry the UK's nuclear deterrent - the Polaris boats HMS Revenge, HMS Renown, HMS Repulse and HMS Resolution.
A Ministry of Defence spokesman said: ""The disposal of nuclear submarines is a complex and challenging undertaking.
"We remain committed to the safe, secure and cost-effective de-fuelling and dismantling of all decommissioned nuclear submarines as soon as practically possible."