Co-operative Bank customers have reacted angrily after a glitch meant payments were taken twice from some small business accounts.

Customers took to social media to complain, with some asking whether the bank had been hacked and one claiming he was “£5k down”.

Co-op Bank said it was aware of a small number of business account holders affected and was working to correct the issue.

“We apologise for any inconvenience caused and are supporting customers during this period.”

According to its website, Co-op bank has about 3.1 million retail customers and 96,000 small business customers.

The lender said that “duplicate, historical transactions” had been appearing in some business customers’ balances.

Customers have reacted with alarm over the missing money, with some claiming they had been pushed them into their overdrafts.

One tweeted: “Utter shambles regarding duplicate historical transactions being taken from customer accounts without any notification from you this has happened.

“Thousands of £ out peoples’ accounts without even notifying customers. Tell us how this will be resolved?”

Someone else said: “I checked my balance after not being able to buy some petrol to notice that I’m now massively overdrawn and have double transactions going out from weeks ago.”

Some have complained of long waits to get through to the bank.

On its X account, Co-op Bank apologised for the distress caused and urged people in financial difficulty to call its business team.

The bank has 50 branches across the UK and about 3,400 staff.

It was part of the wider Co-op Group more than 10 years ago, before splintering off when it fell into deep financial difficulty.

In late May, it agreed to be bought out by Coventry Building Society for £780m in a deal that will return it to a mutual structure.