The process had been due to get under way last Monday (30 September) but was pushed back to allow the CAA to focus on repatriating the 150,000-plus Cook passengers left stranded overseas when the iconic operator collapsed on 23 September.

Operation Matterhorn, the UK’s largest peacetime repatriation programme, was due to be completed on Monday morning (7 October).

The CAA says the process will be the largest refund effort under the Atol scheme in its history, more than three times the size of its previous largest refund operation.

“The CAA has today also launched its online refund claims form for customers affected by the liquidation of Thomas Cook,” said the authority in a statement.

“The form is available on the CAA’s dedicated Thomas Cook website: thomascook.caa.co.uk/refunds. This will be used to refund more than 360,000 bookings for Thomas Cook Atol protected holidays, covering trips that would have been taken by 800,000 people.

“Atol-protected customers who were abroad can also claim for the cost of replacing the Atol-protected parts of their trip, or out-of-pocket expenses as a result of delayed flights. We aim to pay refunds within 60 days of receiving a valid completed claim form.

“In addition, more than 24,000 direct debit repayments are already in process, with all automatic direct debit refunds on track to be returned to customers from Monday 14 October.”

CAA chief executive Richard Moriarty said the authority would “work round the clock” with its partners to deal with the volume of refunds expected.