The building society said that the name, account number, balance and interest earnings of some of its customers were printed on the back of other customers’ statements.

However, Skipton said the risk to affected customers was negligible because the accounts require a customer signature for withdrawals and are not accessible via the internet.

A statemnt from the lender said: “We are writing to those affected to apologise and to reassure them that the correspondence contained insufficient information to enable any unauthorised transactions on their accounts. We are also offering to change the account numbers of any customers seeking additional peace of mind.”