Caledonian Sleeper staff have voted for strike action in a dispute over "appalling" working conditions.

The RMT union said members have suffered workplace stress and mental health issues while morale is at an all-time low following the introduction of its new fleet.

The union said poor staffing levels and insufficient training have contributed to a complete breakdown in industrial relations and "intolerable pressure" on staff.

Members voted by more than 10 to one for strike action and action short of a strike in a turnout of more than 80 per cent, RMT said.

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RMT general secretary Mick Cash said: "Our members on the Caledonian Sleeper are sick and tired of paying the personal price for the botched introduction of the new fleet and that is why they have delivered this overwhelming vote for action.

"It is time for Serco to wake up and take note of the appalling working conditions their mismanagement has lumped on their staff and to take action to resolve this dispute.

"The result will now be considered by the union's executive and we remain available for genuine and meaningful talks."

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Serco Caledonian Sleeper launched its new £150 million fleet on the lowlander route between London and Glasgow/Edinburgh in April.

However, the rollout of the new fleet onto the Highland line has been delayed.

Ryan Flaherty, Serco's managing director for Caledonian Sleeper, said: "We're deeply disappointed by the result of the ballot.

"I believe we have shown a real commitment to dealing with the issues the RMT has raised and indeed there was an acceptance on all sides that progress was being made.

"We remain open and willing to engage in further talks to avoid industrial action and are fully committed to delivering the best possible service to guests."