Firefighters at Sellafield have walked out in a dispute over pay.

The GMB union has planned a 12-and-a-half hour strike between 6am and 6.30pm after it failed to come to an agreement with the nuclear site's management.

Union members, who are also set to strike on Thursday, are picketing outside Sellafield's five gates.

GMB senior organiser Chris Jukes said the situation was "regrettable" but the issue had not been resolved. "The dispute should be settled," he said. "But Sellafield don't seem to want to settle it."

Firefighters, who have said they have been underpaid for years, were due to strike in July but put it on hold as both sides agreed to talk.

Action was then suspended to allow the site's management time to put in place a resolution by the end of last month and both sides have been discussing plans to deal with any serious incident which could take place during a strike.

But the union has accused management of using "stalling tactics".

Mr Jukes said: "Sellafield Ltd management made what GMB believed was an offer in good faith a couple of months ago to resolve this dispute, which dates back years, by introducing a warm zone allowance by the end of September.

"Management have broken their promises with the latest offer at the end of last week.

"GMB’s firefighters have remained professional throughout this process which started in 2012 undertaking all the relevant training courses required, many done on their rest days."

However, a Sellafield spokesman said: "We made an offer to the firefighters which included an additional allowance for carrying out extra work.

"We agreed to work with the GMB and the firefighters to assess the value of that allowance. We remain open to further discussions.

"Our focus is on putting in place arrangements to ensure the site remains safe during any industrial action."

Last month, a separate dispute over pay saw thousands of GMB members go on strike for 24 hours.