Thomas Cook, the 178-year-old global travel group, has collapsed after failing to secure an extra £200 million in funding.
Crucial talks aimed at preventing the holiday firm going out of business were held throughout Sunday but failed to secure the necessary funding with the UK Civil Aviation Authority (CAA) confirming that the tour operator has "ceased trading with immediate effect".
The travel firm, which employs 22,000 staff worldwide including 9,000 in the UK, had been planning to sell 75 per cent of the tour operating business and 25 per cent of its airline to Chinese company Fosun - the company's current largest shareholder.
In the early hours of Monday morning Thomas Cook aircraft were tracked returning to their UK bases and on landing are being parked away from the terminals.
The Thomas Cook website stopped returning holiday booking information with an error message "We're sorry, there are currently no holidays available that meet your search criteria."
Images widely shared on social media show notices are being put on planes by airport authorities to say they are being ‘impounded’.
Some passengers waiting to check in are being delayed with alternative flights arranged with different carriers.
In the UK a massive operation, codenamed Operation Matterhorn, will swing into action with the aim to bring home around 150,000 British people currently on holiday with the firm. On Sunday, empty aircraft had already started to be flown overseas, ready to bring British tourists home on Monday.
Thomas Cook holidays are protected under the ATOL (Air Travel Organiser's Licence) which means travellers on package holidays do not lose their money or become stranded abroad if a travel agent collapses. However this doesn’t apply in the case of people booking flights and accommodation separately.
If you are not covered by the ATOL scheme, you should also contact your credit card company or travel insurer. If you have travel insurance, check your policy for the phrase “airline failure”.
Peter Fankhauser, Thomas Cook's Chief Executive, said the firm's collapse was a "matter of profound regret".
Commenting as the company entered compulsory liquidation, Mr Fankhauser also apologised to the firm's "millions of customers, and thousands of employees".