Supporters of Greenpeace have been reimbursed after a direct debit error that saw donations of 100 times their normal level leave their bank accounts.
On 29 December, thousands of donors already stretched by Christmas spending were hit with direct debit payments of up to £1,000, although the average was between £200 and £300.
The money was returned to supporters on 3 January, but the organisation is now working to refund any bank charges, such as overdraft fees or penalty charges, that might also have been incurred by the donors.
Greenpeace blamed the mistake on a combination of human error and its computer system. The computer key that processes the direct debits in pounds was wrongly pressed instead of the one for pence.
Greenpeace has now changed the system so the mistake cannot be repeated.
Steven Thomson, finance director at Greenpeace, said: "It has been embarrassing for us, but it will have proved more painful for our supporters over the bank holiday period."
The mistake will also be costly for the organisation, Thomson admitted.
He said that losses from repaying donors' bank charges are still being calculated. Although most supporters had been understanding, he expected that a further chunk of money would be lost as disgruntled donors withdrew their support.