A £4bn project to help replace nuclear-armed Trident submarines on the Clyde has been branded as "unachievable" for the third year running by a UK government watchdog.

The Infrastructure and Projects Authority (IPA) has again given the manufacture of new reactors to power replacement submarines its lowest rating of "red" for 2023-24. There are "major issues" that do not seem to be "manageable or resolvable", it said.

The IPA has badged eight other major UK nuclear weapons projects, with a combined overall cost of over £55bn, as "amber". This means they are facing "significant issues" which require "management attention".

These include building new facilities at the Faslane nuclear base, near Helensburgh, and dismantling nuclear submarines at Rosyth in Fife. The construction of the entire future nuclear-powered fleets of submarines - Astute, Dreadnought and Aukus - was also rated amber.

Campaigners attacked the UK nuclear weapons programme as "an unaffordable shambles" and a "disastrous money pit". They have demanded its cancellation, and asked for the money saved to be spent on public services.

The Scottish National Party (SNP) accused the Ministry of Defence (MoD) of being "totally unable" to deliver a cost-effective replacement for Trident on time. The Scottish Greens said that public money shouldn't be wasted on "deadly Cold War hangovers."

The MoD insisted that the Dreadnought programme was "on track" for submarines to start entering service in the "early 2030s". It was working to "improve delivery confidence".

Rolls-Royce, which is making Dreadnought submarine reactors for the MoD, accepted that the work was "challenging". But it said progress was "accelerating" and it was "confident" it could deliver in time.

Trident nuclear project can't be delivered, says watchdog

The IPA's latest report for 2023-24 was published in January 2025, six months late. It assessed the feasibility of 227 major government projects, including 44 run by the MoD with a total cost of £298bn.

Nine of the MoD projects were related to nuclear weapons and submarine programmes, with a total cost of at least £59bn. The one that was given a red rating was to construct reactors to be installed in four Trident-armed Dreadnought submarines to replace ageing Vanguard submarines at Faslane in the 2030s.

The project was also rated as red in 2022-23 and 2021-22, as The Ferret reported. According to the IPA, that means that "successful delivery of the project appears to be unachievable" and it may need its "overall viability reassessed".

It said: "There are major issues with project definition, schedule, budget, quality and/or benefits delivery, which at this stage do not appear to be manageable or resolvable."

The Dreadnought reactors, which are being built by Rolls-Royce in Derby, faced "ongoing challenges associated with achieving the required delivery date" in 2028, the IPA added. This was an "important milestone" for the UK's policy of keeping at least one nuclear-armed submarine on patrol all the time, known as "continuous at sea deterrent".

Among the eight other nuclear projects rated as amber, was a £1.9bn scheme to build new facilities at Faslane and nearby Coulport, on the Clyde, to support new submarines. Its rating was kept secret in 2022-23 and it was red in 2021-22.

Amber is defined by the IPA as: "successful delivery appears feasible but significant issues already exist, requiring management attention". The issues "appear resolvable at this stage" and should not cause delay or increased costs "if addressed promptly".

The Clyde infrastructure project was entering its "most complex phase" over the next four years, the IPA said. It highlighted "two main issues affecting delivery confidence".

One was rebuilding existing facilities while they continue to be used for submarine operations. The other was attracting and retaining suitably skilled staff "to a remote site in a very tight labour market in western Scotland."

Costs of some nuclear projects k...