Image caption The "processing error" affected some payments at the Co-op's food stores and petrol stations

Thousands of Co-op customers who used their cards in the retailer's stores on Tuesday may have been charged twice, the chain has said.

A Co-operative spokesman said a "processing error" had affected its food stores and petrol stations.

Those affected will have their money returned directly to their accounts within the next 24 hours, he said.

The Co-op has apologised and promised to reimburse people who have incurred charges as a result of the error.

Not everyone shopping on Tuesday with Co-op is thought to have been affected and customers who used their credit or debit cards have been advised to check their statements.

'Technical glitch'

The Co-operative spokesman said he was unable to say exactly how many people were overcharged.

Retail analyst David Gray told the BBC that it was a "one-off technical glitch" that "won't do them [the Co-operative] any favours in terms of their brand image".

"Occasionally these glitches do happen; it is just that this is much larger than what we would normally see," he said.

"I don't think customers need to worry too much about making card transactions."

The retailer has 2,800 food stores and 200 petrol stations across the UK.

Its customer careline number is 0800 068 6727.