Staff with Caledonian Sleeper are set to strike over “safety and wellbeing” concerns.

Four days of disruption is expected next month for passengers using the overnight Scotland to London train service after RMT union members were balloted on industrial action and action short of strike.

RMT said there was an "overwhelming ballot result" where members showed a "clear desire" to take industrial action against [operator] Serco's "lack of concern for member's safety and wellbeing" and the company's refusal to negotiate with their union.

But Serco says less than a third of its workforce voted in favour of strike action.

It is the latest issue to hit the service after the Scottish transport secretary said in January that faults with the fleet will take another two months to fix.

RMT said the action was sparked after Serco Caledonian Sleeper continued to provide insufficient berths for rest periods and the company's inability to address the fatigue experienced by staff.

RMT says that safety on the railway is "paramount" and the company are showing a "clear lack of regard for the welfare of its staff".

READ MORE: £100million Caledonian Sleeper fleet delayed again and will not be in service until next year 

"There is no question that RMT members are essential for the safe running of the railway and it is vital that staff are able to carry out their duties responsively and quickly. This can only happen when staff are free from the danger of fatigue," the union said.

Sleeper hosts and team leaders will stage a walkout from 5.30pm on Sunday, October 4 until 5.30pm on Tuesday, October 6.

They will again strike for 48 hours between 5.30pm on Sunday, October 11 and 5.30pm on Tuesday, October 13.

In addition, a ban on overtime, working on days off and undertaking higher-grade duties will also be imposed from October 6-11 and indefinitely from October 13.

Serco said it has “done everything possible” to provide staff with rest areas on board and has also engaged with an independent fatigue specialist to review working patterns.

RMT general secretary Mick Cash said: "Our vote shows that members on SERCO Caledonian Sleeper are absolutely determined to seek justice in this dispute and I am sure this will be displayed by full support across the service for this industrial action.

"A clear message has been sent to management by the vote and now by this call to action. It is now time for the SERCO management to respond in a meaningful and positive way to the serious safety issues at the heart of this dispute.‎"

Ryan Flaherty, Serco’s managing director for Caledonian Sleeper, said: “We have been advised by the RMT that its members intend to take strike action on Caledonian Sleeper services next month. This is despite less than a third of our workforce voting in favour of this in their ballot.

“We are currently reviewing plans for services on the dates in question and will update guests should there be any changes that affect them.

“Since we started operating a reduced programme in March, all staff have received their full wage despite working significantly reduced hours."

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

But it was beset with difficulties including delays botched reservations, broken air conditioning, food shortages and a fault that led to emergency exit windows being locked shut.

In October the independent regulator, the Office of Rail and Road revealed that the Caledonian Sleeper has the worst passenger complaint rate in the whole of the UK.

ORR data for the first quarter of this year revealed that the luxury sleeper service between London and Scotland received 206 complaints per every 100,000 journeys, up by 67% on the previous year.