Caledonian Sleeper workers will strike this month amid claims staff have been placed under "intolerable pressure" due to the "mismanagement" of the rail service.

On Monday, union RMT stated that operator Serco had "reneged on pledges to address a raft of serious concerns raised by staff that have ruined working lives".

However, the sleeper's managing director stated that the industrial action was "completely unnecessary", adding that RMT have been "unable to explain what will bring this dispute to a resolution".

Union members have been told not to book on for any shifts between 12pm on Sunday, September 29 and 11.59am on Tuesday, October 1.

Additionally, members have been instructed not to work any overtime or rest days, not to perform higher grade duties and to work to their original job description from 12am on Wednesday, October 2 onward.

RMT representatives have had a number of meetings with Serco, but claimed that "insufficient progress" had been made - with middle management "openly hostile to finalising a settlement".

RMT general secretary Mick Cash said: "The union is angry and frustrated that promises made to us to address the serious concerns of the Caledonian Sleeper staff at the end of July have not been honoured and that leaves us with no choice but to activate our industrial action mandate.

"‎RMT members have been put under intolerable personal stress as a result of the company's mismanagement of the sleeper service.

"They know it, they have promised to do something about it but they have failed to deliver.

"The move to strike action is entirely Serco's fault and the public will understand that. Everyone knows that when it comes to failure they are global specialists.

"The union remains available for genuine and serious talks."

In response, Ryan Flaherty, Serco's managing director of the Caledonian Sleeper, said: "We are deeply disappointed and frustrated at this industrial action by the RMT, but most of all we are bemused as they have been unable to explain what will bring this dispute to a resolution.

"We have met the RMT and Company Council on many occasions and the changes they have requested have either been completed or are under way, including the recruitment of more staff at Edinburgh, Glasgow and London for a six-month period whilst the new Mark 5 carriages settle in.

"We recognise that the problems we had introducing the Lowland Sleeper were challenging for everyone involved and we are very grateful to all our staff for their efforts and the way they rose to meet the challenge, but we are pleased that in the past weeks the situation has been steadily improving.

"This action is completely unnecessary and we urge the RMT to come back and tell us what they want. We are ready to go to mediation and hold further discussions."