Britain has no records or evidence to suggest that networks at the Sellafield nuclear site were the victim of a successful cyber attack by state actors, the government said on Monday following a report by the Guardian newspaper.

The Guardian reported that Sellafield, which carries out nuclear fuel reprocessing, nuclear waste storage and decommissioning, had been hacked by cyber groups closely linked to Russia and China.

"Our monitoring systems are robust and we have a high degree of confidence that no such malware exists on our system," the government said. "This was confirmed to the Guardian well in advance of publication, along with rebuttals to a number of other inaccuracies in their reporting."

Sellafield, controlled by the government's Nuclear Decommissioning Authority, is located in northwest England and has 11,000 employees.

In a separate statement, Britain's Office for Nuclear Regulation (ONR) also said it had seen no evidence that state actors had hacked its systems as the paper had described.

But the regulator said Sellafield was currently not meeting certain high standards of cyber security it required, adding that it had placed the plant under "significantly enhanced attention.

"Some specific matters are subject to an ongoing investigation process, so we are unable to comment further at this time," the ONR said.

The Guardian report said the ONR was "believed" to be preparing to prosecute individuals at Sellafield for cyber failings.