Thomas Cook has ceased trading, the Civil Aviation Authority says as it launches a programme to bring stranded customers home.
The news comes after the company failed to secure the extra £200m needed to keep it afloat after a day of crucial talks with creditors.
Around one million customers who had travel booked in coming months have been told not to go to the airport, as all bookings, including flights and holidays, have been cancelled.
Peter Fankhauser, the company’s Thomas Cook, said the tour operator’s collapse was a “matter of profound regret”, apologising to those affected.
He said executives had “worked extensively” in an effort to rescue the 178-year-old travel company, adding: “Although a deal had been largely agreed, an additional facility requested in the last few days of negotiations presented a challenge that ultimately proved insurmountable.
“It is a matter of profound regret to me and the rest of the board that we were not successful.
“I would like to apologise to our millions of customers, and thousands of employees, suppliers and partners who have supported us for many years.”
What to do if you’re a Thomas Cook customer
Read what you can do if you’re overseas or had booked a trip with Thomas Cook
The collapse means that the CAA has launched the UK’s biggest ever peacetime repatriation to bring more than 150,000 Thomas Cook customers home.
The programme is expected to last until Sunday 6 October and will rescue almost twice the number brought home after Monarch Airlines failed in 2017.
Richard Moriarty, chief executive of the UK Civil Aviation Authority, said news of Thomas Cook’s failure was “deeply saddening”.
He added: “The government has asked us to support Thomas Cook customers on what is the UK’s largest ever peacetime repatriation.
“We have launched, at very short notice, what is effectively one of the UK’s largest airlines, involving a fleet of aircraft secured from around the world.
“The nature and scale of the operation means that unfortunately some disruption will be inevitable. We ask customers to bear with us as we work around the clock to bring them home.”
Transport Secretary Grant Shapps said the company’s collapse was “very sad news for staff and holidaymakers” and that the government and CAA were “working round the clock to help people”.
Thomas Cook had been one of the world’s oldest and largest travel companies, having been established in 1841 by a cabinet maker who organised a day trip for temperance movement supporters.
According to its website, the group employed 21,000 people in 16 countries, including 9,000 in the UK, operating 105 aircraft and 200 own-brand hotels and resorts.
But it was hit hard by online competition, a changing travel market, terrorist attacks in destinations such as Tunisia and last year’s European heatwaves.