CALEDONIAN Sleeper staff are to vote on industrial action over "potentially dangerous" defects in the iconic Scotland-London service's train fleet.

RMT will ballot its members on strike action and action short of a strike next week after talks with the Sleeper's operator, Serco, broke down.

The ballot will close on December 15, potentially paving the way to major disruption on the cross-Border service in the new year.

The trade union said it had been left with no option but to push members to support a walkout or work-to-rule after the company failed to address a "number of defects contained within the rolling stock".

RMT claims that some of the 200 plus defects are potentially dangerous to the staff on board and the travelling public who are "paying top dollar prices for a service which is unreliable, increasingly uncomfortable and riddled with health, safety and welfare issues".

They cite disconnected smoke detectors, toilets being out of order and broken lighting and heating systems among the faults, along with a series of air conditioning failures in the summer "which left passengers sweltering the sleeping berths".

On some occasions, RMT says train staff have had to carry boiling water through the train while it is moving because water boilers were not working in some carriages, putting staff and passengers at risk of being scalded.

The union said passengers have also had to put up with a pungent smell from toilets and an issue with batteries under some coaches also giving off a strong smell, a loss of power in their accommodation quarters during journeys, and a serious problem with a huge number of wheel flats which has led to some services being completely cancelled and passengers being bussed from Scotland to London instead.

Serco took over the Caledonian Sleeper franchise in March on a 15-year contract. It was previously operated by First Group, under the ScotRail umbrella.

RMT General Secretary Mick Cash said: "The poor service to passengers, in conjunction with the company's failure to address the issues raised by RMT representatives and officials in recent talks, has now reached the point where the union has decided enough is enough and we will now proceed to ballot for industrial action before someone is injured."

He added: "Our members have been unhappy with Serco's management of the iconic service from Scotland to London since the very early days of them taking on this fifteen year franchise. This is yet another example of Serco winning public sector contracts and failing to deliver for the tax payer, passengers and staff. "

Mr Cash said the problems highlighted by the union in relation to the Sleeper franchise should also be a "wake-up call" for the Scottish Government ahead of the awarding of the new CalMac contract next year.

Serco, which also runs the Dubai metro and Australia's transcontinental Indian Pacific rail service, is bidding to take over the running of the west coast ferry service from the incumbent, public sector operator Caledonian MacBrayne.

It was awarded the Sleeper franchise on the promise that it would transform it into a "hotel on wheels", with 75 new state-of-the-art carriages featuring en suite berths and a brasserie-style club car.

However, the new fleet will not be rolled out until 2018.

Peter Strachan, managing director of Caledonian Sleeper, previously said he was disappointed that RMT were considering industrial action. 

He said: "Since taking over running of the Caledonian Sleeper eight months ago Serco has worked hard to improve the service for both our customers and staff."