A "processing error" on Tuesday saw thousands of Co-op customers double charged for card payments, the UK retailer has warned.
"Due to a processing error customers who shopped with us or used a petrol filling station on 7 July using a credit or debit card were charged twice," the company says in a statement.
All those affected will be refunded within 24 hours and anyone who has incurred bank charges because of the error will be reimbursed.
The exact cause of the issue, affecting some 2800 stores, 200 petrol stations and, potentially, hundreds of thousands of people, is not yet known but human error is understood to be to blame.