According to the 'Daily Express, the the couple realised that they had forgotten about their mother when they were on a ferry halfway across the English Channel on their way to France.
The frantic pair phoned Port of Dover police for help.
The woman, thought to be in her 70s or 80s, was found sitting in their car parked in a multistorey and was taken for a cup of tea to await the return of her family, from Bootle, Merseyside, on the next ferry nearly four hours later.
"I cannot recall anything like this before and I've been here for 20 years. The elderly woman, one of their mothers, was absolutely fine," Inspector Neil Care was quoted as saying.
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