Twelve cross-border sleeper trains have been cancelled over a lack of staff and the impact of Storm Arwen.
And the operator Serco said “absences of safety critical staff” have caused the amended timetable and cancellations to Caledonian Sleeper services.
The operator has been in a long running industrial dispute with the RMT union about pay and conditions, but the current disruption, which started on December 3, is not linked.
A Serco spokesperson said Storm Arwen caused some service amendments and cancellations, but those from December 5 are primarily due to sickness and people taking annual leave.
A notice on the Caledonian Sleeper website states that from December 5 to December 9 there will be no service northbound from London Euston to Fort William, a total of five cancelled trains.
Passengers will travel on the Lowlander Sleeper service to Glasgow Central and connect with the 8.23am Scotrail service arriving at Fort William at 12.08pm
From December 6 to December 9, there is no southbound service direct from Fort William to Euston, a total of four cancelled trains.
Passengers who have booked for that service will be bussed to Kingussie where they will join the east coast service from Inverness to Euston.
There were a further three cancellations of sleeper services running from London Euston to Aberdeen between December 1 to 3, making a total of 12 cancelled services up to December 9.
Caledonian Sleeper trains running southbound, on the country’s east side, from Inverness through Edinburgh to London Euston are unaffected by the cancellations.
Magnus Conn, Serco’s operations director at the Caledonian Sleeper, said: “Due to the impact of storm Arwen and absences of safety critical staff scheduled to operate our train services, we have been running an amended timetable this week.
“We have had to make planned cancellations to some of our Northbound Aberdeen services between December 1-3.
“It is our priority to keep our services running, but the safety of our guests is always of utmost importance.
“We are very sorry for the inconvenience caused to all of our guests affected by this disruption, who have all been offered a refund.
“On December 2, some of our services were impacted by an incident at Harrow and Wealdstone.
“We’re sorry to guests who were affected by this, but the cancellations were due to events outside our control and impacted all train operators.
“All travelling guests on the affected services are entitled to refunds via the Delay Repay scheme.”
Serco made no comment about the cancellations between Fort William and Euston and the northbound trains from December 5-9.
RMT regional organiser, Mick Hogg, explained that “safety critical staff” are the train managers, effectively the equivalent of the guard, one of whom works on each of the four services per night.
Mr Hogg said: “In layman’s terms, if there is no safety critical person for the train, it is cancelled on the grounds of safety.
“If a train crashes or is derailed the safety critical role of the guard is to safely evacuate all passengers and call the emergency services particularly if the driver is incapacitated by collision or derailment.”