Passengers on the London to Inverness sleeper were delayed by two-and-a-half hours yesterday after part of a pallet was thrown onto the roof of the train.
Police have launched an investigation into the incident which caused major disruption on the 9.16pm service from London Euston to the Highland capital.
Staff on the Serco-run route received reports of an object on the roof after the train left Preston just after 3am yesterday morning.
Network Rail engineers were called out and the train was stopped in the Barton area.
The overhead cables were made safe and the piece of wood was eventually removed.
On social media, the Caledonian Sleeper’s page initially told frustrated service users that the delay had been caused by “a table that has found its way on to the roof”.
However, it is understood that the wood is now thought to have been part of a pallet, and that the police were yesterday treating the incident as “malicious”.
The train arrived in Inverness 148 minutes late yesterday morning.
Passengers also reported that the sleeper service to Fort William was cancelled and replaced with a bus from Edinburgh.
A spokesman for the British Transport Police said: “We were called at 3.06am on Thursday, December 3, to reports of an object on the roof of the 9.16pm London Euston to Inverness service.
“Staff noticed the object, a piece of wood, on the train roof as it passed through Preston station.
“The train was stopped in the Barton area and overhead cables were isolated while the piece of wood was removed, before the train resumed its journey.
“Enquiries to establish how the piece of wood came to be on the train are ongoing.”
Anyone with information was asked to contact British Transport Police on 0800 40 50 40, or text 61016.
Information can also be passed anonymously to the independent charity Crimestoppers on 0800 555 111.