Services north of Carlisle were cancelled on Wednesday afternoon and did not operate again until around 6am yesterday.
The problem was detected on the Glasgow to Carlisle line, near Gretna, where a lengthy stretch of overhead power lines had been severely damaged, according to Network Rail. The issue was detected around 2pm on Wednesday with all services north of Carlisle axed shortly before the 5pm rush-hour.
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However, a spokeswoman for Network Rail, which runs and maintains the UK's rail infrastructure, said engineers were still baffled over the cause of the damage which is usually associated with high winds in winter.
The problem led to dozens of services in both directions between Glasgow and London being cancelled or delayed, with passengers bused between Carlisle and Glasgow or Edinburgh on replacement coaches.
Sleeper trains were also used as hotels for passengers stranded in either Glasgow Central or London Euston overnight.
Virgin Trains, the main operator on the West Coast Main Line, said 36 of its services were directly affected on Wednesday evening with a further three early morning trains hit by cancellations and delays yesterday. A spokesman said the hundreds of passengers affected would be entitled to claim a full refund.