MSE Update: 4.24pm, 10 July: Co-op has confirmed that all refunds were processed on Thursday evening (9 July). However, when the amount will be credited to accounts depends on shoppers' individual banks' clearing process. So you should contact your own bank to find out when the funds will be available.

Hundreds of thousands of Co-op shoppers have potentially been charged twice in a blunder involving people using their cards in the retailer's food stores or petrol stations. However, the retailer says those affected will be automatically refunded.

A spokesman for the Co-operative says the error occurred on Tuesday. He didn't say how many people were affected but it is thought it could run into hundreds of thousands.

Not everyone shopping on Tuesday with Co-op will have been affected, but the retailer says those who are will have the money for the second incorrect transaction automatically credited directly back to their accounts within the next 24 hours.

If you're unsure about whether you have been affected, you should check your statement now. If the money for the incorrect transaction isn't credited back within the next 24 hours, contact Co-op on 0800 068 6727 to ask for a refund.

The retailer has also promised to reimburse people who have incurred charges as a result of the error, such as overdraft fees. To get this back, again call Co-op on 0800 068 6727.

The Co-op has 2,800 food stores and 200 filling stations across the UK. It says all of them could potentially have been affected and any type of debit or credit card could have been involved.

'Apologise to all those affected'

A statement for the Co-operative Food says: "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.

"We would like to apologise to all those affected, and reassure customers that refunds will be made directly in to their accounts within 24 hours. We will also reimburse any customers who have incurred bank charges as a result of this error. These customers should contact our customer careline."

Co-op shoppers hit with double charge
Co-op card customers hit by double charge