Expected costs of clearing-up nuclear sites in the country has increased by an estimated £2.7bn.

The National Audit Office (NAO) has published a progress report into work the Nuclear Decommissioning Authority (NDA) is undertaking to decommission its Magnox estate.

It includes 10 reactor sites and two research facilities around the UK.

The expected cost of the operation has risen from £6bn in 2017 to £8.7bn.

None of the facilities in question are in the county but they include Chapelcross, near Annan.

The Cumbria-based NDA came under scrutiny in 2017 after a legal challenge made by bidder Energy Solution due to the flaws in the contract for the clean-up awarded to Cavendish Fluor Partnership (CFP).

In March 2017, the Secretary of State for Business, Energy & Industrial Strategy announced that the NDA had agreed settlements totalling £97.3 million with the bidder that brought the legal claims against the NDA.

He also announced that the NDA had decided, based on legal advice, to terminate the contract with CFP nine years early due to a “significant mismatch” between the work specified in the tendered contract and the work that needed to be done.

In September 2019, Magnox became a subsidiary of the NDA.

The NAO report said: "In March 2017, the NDA faced a challenging set of circumstances after the failure of the original Magnox contract. Since then, it negotiated a revised contract with CFP, avoided further litigation and succeeded in maintaining a working relationship with its supplier that led to the completion of £2.72 billion of decommissioning work before the contract ended in August 2019.

"The results of the NDA’s recent work to update the decommissioning programme for the Magnox sites shows that there remains significant uncertainty around its cost, with current estimates ranging from £6.9 billion to £8.7 billion. With the NDA now taking more direct control over the management of its sites, it will be critically important that it builds and retains better knowledge of the condition of its sites to enable it to plan and deliver decommissioning work efficiently and effectively. The NDA considers that it will be better placed to achieve this under its revised delivery model, but it is too early for us to assess the effectiveness of these arrangements."

A spokesman for the NDA said: "We welcome the scrutiny the NAO places upon bodies like ours, and the recommendations it includes in today’s report.

"We are grateful that the Report recognises the way in which we successfully negotiated the end of the contract to manage the Magnox sites, enabling us to move to our improved delivery model.

In September 2019 we successfully transitioned Magnox Ltd into a wholly owned subsidiary of the NDA, and we are seeing good progress being made to clean up our 12 Magnox sites under the leadership of the new CEO, Gwen Parry Jones OBE.

"Ours is a hugely complex and challenging mission in which we’re making progress. The NAO recommendations will help to inform our work, as we continue vital clean-up and decommissioning work across our 17 nuclear sites."