Barclays Bank discovered one day that one of its part-time employees, Mrs Keenan, had been receiving salary at the full-time rate for a number of years. She was being paid £17,000 instead of £9,500. Mrs Keenan had believed that she was receiving the correct salary because she had been promised a pay rise when Barclays took over her previous employer, Woolwich Building Society. Barclays demanded that Mrs Keenan return the overpaid amounts and Mrs Keenan, in turn, brought an employment tribunal claim. The employment tribunal held that Barclays was obliged to continue paying Mrs Keenan at the full-time rate. Mrs Keenan had no actual knowledge of the mistake and could not have been expected to know about it. She genuinely thought she was entitled to the higher salary (Keenan v Barclays Bank Plc).