On behalf of over 13,000 scientists, engineers and professionals in the UK nuclear sector, Prospect National Secretary Mike Graham said: "We wanted an end to the uncertainty for the workforce in EnergySolutions UK.

"The ideal would have been for a quick deal that did not distract from the company's core activity of managing the UK's 10 Magnox reactor sites, or cast a shadow over the competition for the next seven-year decommissioning contract, recently launched by the Nuclear Decommissioning Authority.

"News that any sale is now off raises further questions. Are the staff in EnergySolutions UK to be left in limbo until a new contract is awarded in 2014? Will additional transitional arrangements be introduced to ensure the focus remains firmly fixed on the safe and efficient clean-up of sites?

"We need urgent answers and reassurances over the ongoing stability of the organisation and will be raising the issue with the Department of Energy and Climate Change."