The Civil Aviation Authority believes fraudsters have been seeking to undermine its refund operation, and has reported its concerns to the police.

The CAA began the largest ever Atol refund operation yesterday morning, as it looks to reimburse 360,000 forward bookings for a total of 800,000 passengers.

About 60,000 claims were made on the first day of the refund scheme, and around 100,000 were made by Tuesday lunchtime.

However, the CAA is insisting customers only use its official channels as it suspects scammers of attempting fraudulent activity in relation to the claims process.

Chair Dame Deirdre Hutton said: “This morning we have taken urgent action in response to what we believe is attempted fraudulent activity in relation to refunds for Thomas Cook customers. If you have made a claim directly with us, then your claim is being processed and you do not need to take any action.

“Our role is to protect the consumer and this is our foremost priority. We will not hesitate to take the necessary action to do so. Therefore, please only make claims directly through the official dedicated website: thomascook.caa.co.uk/refunds

“Please help us to combat the risk of fraud by not submitting your details to any other website. Our focus is on getting money back to the right people as soon as possible and combating fraud in every way possible.

“We are informing the police of this activity and are implementing further verification checks to protect consumers. Where we see evidence of fraud, we will seek to prosecute any individuals or organisations involved.

“We will publish further updates as soon as more information is available, and we remain committed to processing refunds to Thomas Cook customers quickly and securely.”