THE UK’s £31 billion programme to replace Trident submarines is in major doubt, according to a high-level government spending watchdog.

A report by the Infrastructure and Projects Authority (IPA) to the Treasury and Cabinet Office has warned that the plan to build four new nuclear weapons submarines for the Clyde is in danger because of a number of "major risks in key areas".

This is despite the overwhelming vote in the House of Commons last month in favour of replacing Trident. The plan was opposed by every Scottish MP, except for the lone Tory, David Mundell.

The poor assessment of the Trident programme’s prospects was buried in a report about 143 projects published online by the IPA several days before the vote at Westminster. It gave the submarine successor programme its second worst rating of “amber/red”.

This means that the project is judged to be running into serious difficulties because of cost overruns, management problems and technical issues. "Successful delivery of the project is in doubt, with major risks or issues apparent in a number of key areas,” said the IPA.

“Urgent action is needed to address these problems and/or assess whether resolution is feasible.”

According to critics, costs have already risen by between £15bn and £20bn. The planned date for bringing the submarines into service has been delayed from 2024 to the “early 2030s”.

This has forced the Royal Navy to extend the lives of the four existing Trident-armed Vanguard submarines, based at Faslane near Helensburgh. They originally had a design life of 25 years, but are now due to be kept on patrol for 38 years.

The programme has also been plagued by skills shortages, and suffered a serious mishap with the reactor that drives the submarines. There has been a major restructuring of the defence nuclear programme within government.

As well as condemning the Trident replacement programme, the IPA rated plans to build seven new nuclear-powered Astute submarines as amber/red. A submarine reactor-building project by Rolls-Royce in Derby was classified as amber, suggesting it has "significant issues" requiring management attention.

The IPA’s assessment of the state of another major programme to upgrade the nuclear warheads for Trident missiles has been kept secret. This is to safeguard national security and avoid prejudicing the defence of the realm, it said.

The SNP warned that “the whole obscene project” was now completely out of control. The total costs could top a “terrifying” £200bn, according to the defence spokesperson, Brendan O’Hara MP.

“Now we hear that that the alarm bells are ringing about the ability to deliver the programme at all without urgent action,” he said. “(Prime Minister) Mrs May has just put a halt to Westminster’s other nuclear obsession – Hinkley. Perhaps she should take this opportunity to do the same and review the useless, immoral and now clearly out of control Trident programme.”

On July 28 new British Prime Minister, Theresa May, launched an unexpected review of plans for a new nuclear power station at Hinkley in Somerset. She had been expected to give it the go-ahead after the French state company, EDF, made a final decision to invest in the project.

Peter Burt from the campaign group, Nuclear Information Service, said the IPA report confirmed that Trident was in trouble. “The Ministry of Defence's (MoD) track record on undertaking major equipment programmes is littered with failures and cock-ups,” he said.

“The MoD’s ancient and rickety nuclear infrastructure is not up to the job of replacing the Trident nuclear weapons system and the solution that the government has favoured up till now – throwing money at the problem – quite simply isn't going to be enough to solve the fearsome technical problems that the project faces.”

According to John Ainslie, coordinator of the Scottish Campaign for Nuclear Disarmament, the amber/red rating meant that the MoD couldn’t control rising costs and won’t be able to build new submarines on time. “Normally when you see an amber or red light you should stop,” he said. “The government is pushing ahead with their nuclear weapons’ programme despite the obvious risks. They should be pulled over for reckless driving.”

The MoD pointed out that it was setting up new organisations to manage the submarine replacement programme. The industrial and commercial arrangements were also being changed to better control funding and delivery.

Although the cost of the four new submarines was estimated at £31bn, there was also to be a contingency fund of an additional £10bn. This was “a prudent estimate based on past experience of large, complex projects”, the MoD said.

The amber/red rating “recognises the complexity and scale of delivering the most advanced submarines ever commissioned by the Royal Navy, the ultimate guarantee of our national security,” an MoD spokeswoman told the Sunday Herald. “We are determined to get the successor programme right, that’s why we have established a new Director General Nuclear sponsor organisation and will set up a new submarine delivery body.”