A train crosses the river Thames in London
FILE PHOTO-A train crosses the river Thames at sunrise as British railway workers strike over pay and conditions, in Richmond, London, Britain, February 3, 2023. Reuters

Thousands of railway workers in Britain will go on strike on May 13 after the RMT trade union rejected the latest pay offer by train companies, an escalation in a long-running dispute that has caused disruptive strikes since last summer.

The National Union of Rail, Maritime and Transport Workers (RMT) said on Thursday it had received a clarification from train operators, which meant a first-year payment of 5% would only be effective if the RMT ended its industrial mandate, meaning no further strikes could take place.

The Rail Delivery Group (RDG), which represents Britain's train operators and had made a new offer to RMT railway workers earlier this month, did not immediately respond to a request for comment.

"The RDG have reneged on their original proposals and torpedoed these negotiations," RMT General Secretary Mick Lynch said. "Therefore, we have no alternative but to press ahead with more strike action and continue our campaign for a negotiated settlement on pay, conditions and job security."

The new 24-hour strike comes after the RMT had cancelled two planned nationwide strikes for March 30 and April 1 while it considered the latest pay offer.

The May 13 strike will coincide with the grand final of the Eurovision Song Contest in Liverpool for which thousands of visitors are expected.

Railway workers are among hundreds of thousands across Britain including teachers, doctors, nurses and civil servants who are in pay disputes with their employers as inflation hovers around 40-year-highs of about 10%.

The RMT said it was re-balloting its members, who work for 14 British train companies, for a mandate for further industrial action.

"We will then put on a further programme of strike action to make the employers and the government who continue to hold the puppet strings, see sense in this dispute," Lynch said.