Queues formed outside a Tesco store in London last week after a faulty cash machine began issuing double the money requested by customers.
An "operational error" led to the ATM - outside a Tesco Express in Cranford, Hounslow - dispensing £20 notes instead of £10 notes.
According to press reports, a lengthy queue quickly formed at the machine, with customers phoning friends and family.
Tesco - renowned for its 'every little helps' slogan - says it will not try and recoup the money.