Gary
Found this...........
It is a legal requirement to pay the money back - the criminal offence is to "retain a wrongful credit".
Theft Act 1968 S.24A Retaining a wrongful credit
Off the top of my head it is an offence to knowingly retain a wrongful credit and dishonestly fail to take steps to rectify the wrongful credit.
"It is 'wrongful' if it is the credit side of a money transfer obtained contrary to S15A (Theft Act 1968).
It is also 'wrongful' to the extent that it derives from:
a) theft;
an offence under S 15A (obtaining a money transfer by deception);
c) blackmail;
d) stolen goods".
By the definition of the law, it looks as if the meaning of 'wrongful' does not easily indicate on this occassion an error or miscalculation but in this case the proceeds of a criminal act.
For those scurrying around to look up the S15A ....
"A person is guilty of an offence if by any means he dishonestly obtains a money transfer for himself or another."
Is it dishonest, as he didn't ask for the money nor did he decieve anyone into doing anything that would have gained him the swag.
My understanding is you have to repay the money but you are allowed to retain any interest accrued on the amount deposited.