The UK government has apologised to thousands of Thomas Cook passengers waiting for holiday refunds after the travel company's collapse in September.
Paul Smith, director at the Civil Aviation Authority, the body responsible for the refunds, said it was “very sorry" and promised the CAA is "working tirelessly" to process payments.
The CAA originally said all valid claims made on the first day of its refund programme, opened on 7 October for customers covered by Atol-protected insurance, would be paid within 60 days. But they have since confirmed that only two-thirds would be paid on time, with many passengers yet to provide further details needed to secure refunds.
Although the CAA has managed to refund £160m, more than 50,000 customers are still owed money.
The government body has put the delays down to incomplete claim forms and attempted fraud.
But customers were frustrated that they received requests for further information to help their claim just days before they were expecting their money back.
"This is the biggest refund operation in UK travel. We have paid out already about £160m, and expect over the next couple of days to get that up above £180m,” Smith said.
"We have had to put some extra checks in because we were concerned about fraud. And we had some challenges with the data we received from the company. We are sorry for those people we have not yet been able to pay."
At least 300,000 Thomas Cook claims have been made so far, 215,000 of which have been confirmed as valid. However, this figure includes about 90,000 direct debit customers whose money was automatically returned in October.