The UK's nuclear weapons programme is £1.3 billion over budget due to delays caused by poor management, a Government spending watchdog has warned.
The National Audit Office (NAO) said the Ministry of Defence's (MOD) failure to learn from past mistakes meant key projects to upgrade the Defence Nuclear Enterprise were over budget and behind schedule.
Three key nuclear sites were assessed by the NAO in the report.
It said "inappropriate" contracts with external contractors and beginning building work on facilities before the designs were "sufficiently mature" had added hundreds of millions of pounds to costs.
The watchdog also highlighted a lack of technical skills within the MOD.
The findings come as the Prime Minister's chief adviser Dominic Cummings prepares to launch a review into defence procurement.
Mr Cummings, who has been critical of previous MOD projects, has already held talks with Defence Secretary Ben Wallace.
Which programmes were assessed in the NAO's report?
- Project Mensa to construct a new nuclear warhead assembly and disassembly facility at the Atomic Weapons Establishment site at Burghfield
- The building of a new core production capability (CPC) at the Rolls Royce site at Raynesway to produce the latest nuclear reactor core designs
- The primary build facility at the BAE Systems shipyard at Barrow-in-Furness where the new Dreadnought class submarines to carry the Trident nuclear missiles will be built.
The three projects assessed in the report, which included BAE Systems' submarine building facility at Barrow-in-Furness, were valued at £2.5 billion.
But the NAO found the costs had risen by £1.35 billion after delays between 1.7 years and 6.3 years.
The NAO said it was "disappointing" that the MOD was continuing to repeat mistakes made in the 1980s and 1990s.
Similar problems had also been encountered in UK civil nuclear projects and US defence programmes, but the NAO said it had found no evidence of lessons being shared or learned.
Among the specific problems highlighted, the NAO said delays to project Mensa had meant the MOD having to spend an additional £21 million keeping existing facilities going.
However, the report also acknowledged the MOD is making progress with the projects.
Gareth Davies, head of the NAO, said: "Although [the MOD] has recently introduced changes to enhance its oversight of the projects and improve its contracts with suppliers, it should have learnt earlier from past mistakes and the experience of others in the nuclear sector.
"Instead, the MOD's failure to mitigate commercial and delivery risks early on has led to project delays and cost increases, as well as impacting its wider work."
An MOD spokesperson said the department was "carefully examining" the report.
“We are committed to strengthening the management of nuclear programmes, including investing significantly in infrastructure and working closely with regulators and industry partners,” the spokesperson added.
Cover image: Submarine HMS Vengeance (Picture: MOD).