British Transport Police officers were 1.42am on Tuesday following reports that two young men aged 17 and 18 had gained access to the locomotive.

They were thought to have sneaked onto the train in the middle of the night after tampering with the signalling system.

Officers said some packages had been “interfered with”, although nothing had been stolen. Both youngsters have been charged with malicious mischief, theft and threatening and abusive behaviour.

The signal tampering caused significant disruption on the west coast mainline between Carlisle and Lockerbie.

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In a statement the British Transport Police said: “Officers were called to the line in Lockerbie at 1.42am this morning following reports that two young men had gained access to a Royal Mail train, damaging signalling equipment in the process.

“Officers attended and a 17-year-old and an 18-year-old were located in a carriage and arrested.

“At this stage it’s not believed anything was stolen but a number of parcels in the carriage had been interfered with.

“Both young men have been charged with malicious mischief, theft and threatening and abusive behaviour.”