SOME of them last saw service more than 30 years ago and should have been disposed of shortly after being decommissioned.

Now spending watchdogs have condemned defence chiefs for their “dismal” failure to scrap its rusting fleet of obsolete nuclear submarines.

Ministry of Defence chiefs have admitted it will take until the late 2060s to defuel and dismantle 20 disused boats currently in storage, seven in the Rosyth yard on the Forth.

But the UK’s main financial watchdog has warned there are are still no plans for how to dispose of submarines currently at sea, including the four Vanguard-class Trident missile carriers.

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In a scathing report, the National Accounts Office (NAO) detailed a history of soaring costs, prolonged delays and technical indecision about what to do with the obsolete subs.

The MoD has now estimated over the next 120 years it will need £7.5 billion to maintain, dismantle and defuel its decommissioned nuclear submarines and 10 more currently at sea. The bill for each boat is estimated at under £100m.

Labour MP Meg Hillier, the 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 before we run out of space to store and maintain submarines and we damage our reputation as a responsible nuclear power.”

Nine of the vessels – all at Devonport near Plymouth – still contain irradiated fuel. No boat has been defuelled since 2004 after a regulator ruled the UK lacked the facilities to do so. The MoD is currently trying to recreate a capacity to remove fuel from the submarines. In 2007 the price for this was estimated at £175m. It is now expected to cost £275m.

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A deadline for getting such technology up and running has gone from 2012 to 2023, while the average number of years submarines have been stored with fuel is nine years.

All stored submarines are at facilities run by the engineering company, Babcock. It has seven boats at its Basin Three at Rosyth in Fife which all have had their nuclear fuel removed. The oldest, HMS Dreadnought, has been at the site since 1980. The others were decommissioned in the 1990s and are Churchill and Swiftsure and the old Polaris nuclear missile boats, Revenge, Resolution, Renown and Repulse. NAO in its report said it was unclear whether there would be space for the bigger Trident submarines at Rosyth.

Environmentalists have been warning that authorities just have not figured out how to deal with their old nuclear-powered boats. Five years ago Greenpeace said “the UK has failed to identify a long-term storage disposal option for nuclear waste and that this problem will not be solved within the coming decades”.

Delays have not just hit defuelling as dismantling is also way behind deadline. NAO said the MoD’s deadline for ruling out a tested dismantling scheme had stretched from 2011 to 2026.

The report continued: “In 2013 the department also outlined its requirement to ‘dismantle 27 defuelled submarines by 2050 in a safe, secure and sustainable manner which upholds reputation as a responsible nuclear operator’. Following delays, it now estimates to fully dispose of these submarines by the late 2060s, up to 19 years later than envisaged, and roll out its approach by 2026, representing a 15-year delay.”

America, France and Russia dispose of submarines by removing an entire reactor block. The US has scrapped more than 100.

The NAO warned new ways of breaking up newer boats would also have to be developed. It said: “The department does not have a fully developed plan to dispose of Vanguard, Astute and Dreadnought-class submarines, which have different types of nuclear reactor. Within the civil nuclear sector, organisations must consider waste disposal during the design stage. The department does not have a similar obligation.”

A MoD 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 as soon as practically possible.”