A man reportedly 'almost fainted' when a ticket inspector informed him he owed £1,048 for train tickets to London - after boarding the wrong train.
The man was travelling with 38 family and friends who had pre-paid London Midland tickets from Birmingham New Street to London Euston.
But they accidentally boarded a 10.30am Virgin Trains service on Monday instead.
A ticket inspector discovered their error and gave the group the option of paying £800 to travel to the next stop - 100 miles away in Watford - or face a heftier fine and possible court prosecution.
They paid the full amount to complete their journey to London Euston.
An onlooker told the Birmingham Mail: "It was a pretty heart-stopping moment.
"He looked a little faint and I'm not surprised really, I mean, it's such a lot of money.
"The inspector was very matter of fact about it all and I understand he was doing his job – but it was an honest mistake.
"I think allowances should be made when it does look like a genuine error."
Virgin Trains said the group could have saved more than £600 if they had booked with them in advance.
"That would mean all 39 could have travelled for a maximum price of less than £300.
"Unfortunately, if passengers have booked to travel with another operator their tickets are not valid on Virgin Trains' services."
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