Delays to major projects at Sellafield are expected to reach almost £1 billion, according to a damning report which attacks the Nuclear Decommissioning Authority’s ability to clean-up the site.

The Public Accounts Committee (PAC) report found that most of the major projects at the complex West Cumbria site were still “significantly” delayed or overbudget, with over-runs of £913 million expected.

The committee – which last examined progress at Sellafield in March 2015 – said it remained sceptical about the Nuclear Decommissioning Authority's (NDA) long-term strategy to decommission the complex site in West Cumbria.

"We are not convinced that the NDA is achieving the wider economic benefits that would help justify the vast amounts of public investment at Sellafield,” the Nuclear Decommissioning Authority: Risk Reduction at Sellafield report said.

In its latest report, the committee did say that some progress had been made in the last few years, with cuts in delays and costs for 14 major projects with a combined lifetime cost estimated at £6bn.

But it warned that there was a long way to go, accusing the NDA of failing to systematically review why major projects kept running into difficulties, and failing to properly analyse the constraints preventing faster progress.

Sir Geoffrey Clifton-Brown, deputy chairman of the committee, said: "This report is critical of the NDA’s performance. The Government's oversight of the NDA's performance could and should be much better, particularly on projects at Sellafield that cost a considerable amount of public money.

"This report follows the committee's earlier report into the NDA's Magnox contract. The NDA failed in both the procurement and management of this contract and cost the taxpayer £122 million."

He added that the Department for Business, Energy & Industrial Strategy (BEIS) needed to "seriously get a grip" on its oversight of nuclear decommissioning, with the committee recommending that BEIS publish an assessment of the NDA's performance every three years.

The report added that NDA had cancelled three projects since 2012 after spending £586 million of taxpayers' money on them.

The NDA said it welcomed the PAC report and would be responding in full to its recommendations.

In a statement it said: “The report recognises that since 2015, when the NDA announced its intention to make Sellafield Ltd a subsidiary of the NDA, significant milestones in reducing risk at our largest and most hazardous site have been met.

“It also recognises the improvement that has been made in reducing delays and expected cost overruns.

“Building on this improving trajectory and finding more efficient ways to deliver the challenging work at Sellafield remains the collective priority of the NDA and Sellafield Ltd.

“Cleaning up the UK’s early nuclear sites requires significant public investment and we welcome the scrutiny of the Public Accounts Committee, which plays a vital role in reviewing the efficiency and effectiveness of public spending.

A BEIS spokesperson added: “Decommissioning is an important part of the nuclear cycle and, as the PAC recognises, considerable progress has been made at Sellafield.

"This includes strengthening the governance structure and greater use of cutting-edge technologies to ensure the highest possible safety standards are maintained, whilst reducing the costs of decommissioning by 20 per cent by 2030.”