Managers at Eurotunnel had to apologise "profusely" after passengers were left in their vehicles and forgotten about by staff, forcing the travellers back to England rather than continuing on with their intended journey.
About 20 passengers took the trip to France and back again without being able to get off their shuttle train.
The problem for the unlucky passengers would have been compounded had the breakdown in communications by Eurotunnel staff been accompanied by a car breakdown, highlighting the importance ofcar breakdown cover.
Seven vehicles were loaded behind a wagon that had been left empty after an earlier fuel spill.
The train went through the Channel Tunnel from Folkestone to Calais.
The front vehicles were unloaded by Eurotunnel staff at Calais, who did not realise there were seven cars behind the empty wagon.
The unfortunate passengers ended up travelling back to Folkestone where red-faced Eurotunnel management staff met them, apologised and got them to Calais on the next available train.
The passengers, who had originally left Folkestone at 8.50am last Saturday, were given a refund and also a free crossing in the future.
A Eurotunnel spokesman said: "We have apologised profusely. Something like this has never happened before in our 16-year history and it's very embarrassing for us."
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