Workers on Greater Anglia are to stage a fresh strike in the long-running dispute over the role of train guards, on the day of the 2,000 Guineas horse race at Newmarket.

Members of the Rail, Maritime and Transport union (RMT) will walk out on May 5, followed by a period of refusing to work extra Sundays beyond their agreed rosters.

RMT leaders said they had received the company’s “best and final” proposals, which the union described as “unacceptable”.

RMT general secretary Mick Cash said: “The vital safety role of guards is still under threat and the extension of driver only operation remains a serious risk.”

In a message to members, Mr Cash said: “Greater Anglia remains adamant that the role of the guard will have no involvement in the releasing or closing of train doors.

“The proposal stipulates that ‘train drivers will operate the train doors and undertake train dispatch in normal circumstances’.

“Your union reps are of the view that the company cannot be trusted to preserve a safety critically trained employee, let alone a guard on every train.”

The union is embroiled in similar disputes with South Western Railway, Southern, Merseyrail and Arriva Rail North.

A protest will be held in Westminster on April 25 to mark the second anniversary of the start of the dispute on Southern.

Greater Anglia said conductors were on 40% of its services. The remaining services, mainly commuter trains to London Liverpool Street from Essex, Cambridge, Hertfordshire and Suffolk, did not have conductors.

“We will continue to run a full service during any proposed strike action using stand-in conductors,” the company said.

“Our stand-in conductors have been trained to the same standards as our usual conductors for the routes that they operate.”

Greater Anglia managing director Jamie Burles said: “We are very disappointed that the RMT has announced a strike on May 5.

“In recent weeks, we have had constructive talks with RMT union officials and discussed at length a proposal which we hoped would result in an agreement with the RMT.

“Unfortunately, the RMT has now decided to discontinue those discussions and announce a strike day.

“Our position remains the same. We highly value our conductors, we’re keeping them on our trains, but we want them to concentrate on customer service rather than opening and closing doors.

“We will continue to attempt to talk to the RMT to try to find an acceptable solution.”