While they glide beneath the waves as part of the UK’s nuclear deterrent, they are the pride of the Royal Navy.

But when their service is over, they are unceremoniously left to rust, creating a costly radioactive legacy the Government has shirked for decades.

Just how bad the problem of Britain’s obsolete nuclear submarine fleet has become is today spelled out in a withering report by MPs.

It warns the UK is rapidly nearing a “crisis point” after failing to dispose of a single one of the 20 nuclear submarines decommissioned since 1980 because of a series of short-sighted, and ruinously expensive, spending decisions.

In a scathing commentary on the issue, the House of Commons Public Accounts Committee says the “glacial” pace of the Ministry of Defence has led to “extortionate” storage costs of £30 million a year, which now total £500m.

With the Devonport docks having space for just two more boats, and four more Trafalgar class submarines due to leave service soon, the basin could “reach capacity” in a few years, it warns.

The problem is exacerbated by a £7 billion “black hole” in MoD funds over the next decade, which left MPs “unconvinced” that the money would ever be found for the disposal work, or that the MoD had done everything it could to secure it. 

The committee’s verdict draws on a recent report from the National Audit Office into the MoD’s shortcomings in relation to the disposal programme.

That found the MoD had spent half a billion pounds storing the retired vessels at Devonport in Devon and Rosyth in Fife because of repeated delays, poor decisions, and skill shortages. In their new report, the MPs warn the MoD looks “increasingly likely to find itself without any further storage space by the mid-2020s”.

They say it is “rapidly approaching crisis point and simply cannot afford any further delays, particularly as much of the money currently being spent on the project is not going directly towards either defueling or dismantling,” but to storage and maintenance.

The MPs also say the MoD will miss its goal of dismantling its first submarine in 2023 by at least three years.

They blame the MoD for repeatedly making decisions based on “short-term affordability” which have ultimately increased costs in the longer term and led to “poor value for money”.

The estimated cost of disposing of a single submarine is £96m and the MoD’s future liability for maintaining and dismantling its 20 stored and 10 in-service boats is £7.5bn. 

Devonport is meant to remove the nuclear fuel, but this operation was suspended since 2004 because the facility failed the latest nuclear standards, and nine of the 20 boats still contain irradiated fuel.

The dismantling of the boats and the removal of lower level radioactive parts is supposed to happen at both Devonport and Rosyth.

But the “defueling” part is 11 years behind schedule and dismantling is 15 years late and 50 per cent over budget.

Twelve of the 20 obsolete subs are stored at a purpose-built water basin Devonport, which has a capacity of 14.

The MoD is confident it can get  approval to store 16 boats on site, extending its capacity to the mid-2030s, but if it can’t, there will be a big problem.

On a more positive note, the MPs said there was, finally, a renewed sense of momentum around disposal, but the MoD still had “some way to go” to make the process a routine part of its business.

They recommended the MoD update Parliament annually on its progress, work with project contractor Babcock to train more engineers in decommissioning, and set milestones to avoid running out of storage space, including striking a commercial deal for defueling by the end of 2019.

Meg Hillier, the Labour chair of the committee, said: “Yet again, the Government has failed to see the bigger picture. In an attempt to save money in the short term by delaying the defueling and dismantling of retired nuclear submarines, the MoD is now spending £30m on a year of taxpayers’ money on storage and maintenance.

“The MoD has spent £500m since 1980 on such storage and maintenance. This is simply unacceptable. Whilst some progress has been made recently with submarine disposals, the MoD cannot afford to fall any further behind.

“The Public Accounts Committee has set out a series of milestones for the MoD to ensure that it keeps on track to establish submarine disposal as a routine part of its business.”

SNP committee member Douglas Chapman, whose Dunfermline and West Fife constituency includes Rosyth, said: “This report is a damning indictment into how successive UK governments have failed to deal with the defueling and dismantling of submarines. Action should have been taken on this decades ago, but putting off the decision has had long-term consequences, costing the taxpayer an eye-watering sum to maintain these machines in storage.

“This task is not a lumbering chore, but an opportunity to create jobs and take advantage of the skill-set in Scotland – including West Fife in my own constituency, where some of the subs are stored.

“The Tories need to wake up and work with contractors to ensure a constant stream of work to safely dispose of these redundant boats and to make ensure there is no further delay – and cost to the public purse.”

An MoD spokesperson said: “As the committee acknowledges, the disposal of nuclear submarines is complex, but we are committed to ensuring they are disposed of safely, securely and cost-effectively and have already made progress.”