Travel firm Flights and Fly has ceased operating, the Civil Aviation Authority confirmed.
The Surrey-based company Surrey traded as Cheaplights360, City Breaks, Dial and Fly, Fare Advisor, Fare Comparison and Trip Makers under the websites dialandfly.co.uk and flightsandfly.co.uk.
It was licensed under the Atol scheme managed by the CAA.
But the company may also have sold flights that were not covered by its Atol, the regulator said.
Confirming the failure, the CAA said it was “working to collate information and will publish further information for consumers shortly”.