A new law which will see police officers who protect Sellafield working until they are 65 is being challenged in the High Court.

From next April, Civil Nuclear Constabulary (CNC) officers will have to work until they are 65, and eventually 68, to receive their pension - most UK police can retire at 60.

But the Civil Nuclear Police Federation says it will be "physically impossible" for officers in their mid-60s to protect the public from terrorism.

The body, which represents 1,250 armed police officers at UK civil nuclear sites, is taking its case to London's High Court to try to get the rule changed.

The federation says its officers have the most physically demanding role in the police service and will not be able to maintain their standards of fitness and weapons proficiency into their 60s.

It is asking the High Court to determine whether or not its members are "members of a police service" for the purposes of Section 10 of the 2013 Public Services Pensions Act and therefore entitled to the same retirement age as other police officers in the UK.

The federation has said that if such a ruling is not granted, under changes to public service pensions due to take effect next April, officers could eventually have to work until they are 68 in line with government policy for public service employees.

Chief executive of the Civil Nuclear Police Federation Nigel Dennis said it was "regrettable" that it had been forced to take legal action.

He said: "As yet we have been unable to get a decision from government to accept our professionally-supported argument that it is almost physically impossible for a CNC officer to serve beyond 60.

"What seems not to be understood is that our members are fully-trained authorised firearms officers. The high standards of physical fitness and weapon proficiency are mandatory throughout a career in the CNC and are increasingly difficult to maintain as officers age.

"This makes our force unique within UK policing, as in other forces firearms officers can relinquish their weapon authorisation at any time and all UK officers can retire at 60, a decision made by the present Prime Minister Theresa May when Home Secretary in 2011.

"As a police force the CNC is the fittest body in the UK because of our role in protecting nuclear assets and our more recently acquired role of protecting the wider public against terrorist outrages.

"It makes no sense that we should be saddled through inappropriate legislation with a retirement age which we have little or no hope of reaching. Neither can I believe that the public will feel protected if eventually we have aggressively-armed police officers in their mid-60s being deployed against terrorists."

A spokeswoman for the CNC could not confirm the number of staff affected at Sellafield for security reasons.

She added: “Until the ruling of the Judicial Review is made, it would be inappropriate to comment further at this stage.”