The walkout, which workers say is about guaranteeing customer safety, could disrupt Christmas travel plans.

Workers on the UK’s South Western Railway are to strike for 27 days before the end of the year in the long-running dispute over guards on trains.

Members of the Rail, Maritime and Transport union will walk out for 27 days between December 2 and New Year’s Day, threatening travel chaos for commuters and Christmas shoppers.

RMT General-Secretary Mick Cash said: “Our members have been left with no choice but to call a further 27 days of strike action on South Western Railway.

“At the last meeting we held with SWR, principles in agreements were made in good faith with the company’s negotiating team and we now feel hugely let down again.

“As long as the company continues to refuse to give assurances on the future operational role of the guard, we will remain in dispute.

“I want to congratulate our members on their continued resolve in their fight for safety and the role of the guard on SWR.

“It is wholly down to the management side that the core issue of the safety-critical competencies and the role of the guard has not been agreed.”

RMT members will not book on for duty from 00:01 GMT on Monday, December 2 until 23:59 GMT on Wednesday, December 11, from 00:01 on Friday, December 13 until 23:59 GMT on Tuesday, December 24, and from 00:01 GMT on Friday, December 27 until 23:59 GMT on January 1.

The RMT accused the company of “dangling” a potential breakthrough deal in front of the union and then failing to honour it, offering no reasons for the delay.