Monarch Airlines has been forced to cancel all bookings, including flights and holidays, following a decision by the CAA not to renew its licence to operate.
The carrier become the largest ever airline in the UK to enter administration.
As all of Monarch’s flights due to depart from the UK have now been cancelled, customers should not go to their UK airport, the CAA said in a statement.
However, all affected customers still in the UK should check the CAA website for further information.
Around 110,000 Monarch passengers are currently thought to be overseas.
Due to this unprecedented number, the CAA and government are securing a fleet of more than 30 aircraft, flying to more than 30 airports, to bring people back to the UK at no cost to them.
This is the equivalent of operating, at very short notice, one of the UK’s largest airlines, the CAA said.
Customers currently overseas should check for confirmation of their new flight details which will be available a minimum of 48 hours in advance of their original departure time.
Andrew Haines, chief executive of the CAA, said: “We know that Monarch’s decision to stop trading will be very distressing for all of its customers and employees.
“This is the biggest UK airline ever to cease trading, so the government has asked the CAA to support Monarch customers currently abroad to get back to the UK at the end of their holiday at no extra cost to them.
“We are putting together, at very short notice and for a period of two weeks, what is effectively one of the UK’s largest airlines to manage this task.
“The scale and challenge of this operation means that some disruption is inevitable.
“We ask customers to bear with us as we work around the clock to bring everyone home.”
The CAA will be providing regular updates as our flying programme develops.
Transport secretary Chris Grayling said: “This is a hugely distressing situation for British holidaymakers abroad - and my first priority is to help them get back to the UK.
“That is why I have immediately ordered the country’s biggest ever peacetime repatriation to fly about 110,000 passengers who could otherwise have been left stranded abroad.”
Blair Nimmo, Jim Tucker and Mike Pink from KPMG have been appointed joint administrators to Monarch Airlines.
At the same time, Blair Nimmo, Jim Tucker and Steve Absolom from KPMG have been appointed joint administrators to Monarch Travel Group.
The group’s engineering operation, Monarch Aircraft Engineering, is not in administration and continues to trade normally.
Consequently, all flights operated by Monarch Airlines from the UK, and all future holidays booked with Monarch Travel Group, are cancelled with immediate effect.
Monarch will not be able to reschedule these flights or holidays.
Passengers due to fly with Monarch from the UK are advised not to travel to their airport, unless they have booked alternative arrangements.
Nimmo said: “Mounting cost pressures and increasingly competitive market conditions in the European short-haul market have contributed to the Monarch Group experiencing a sustained period of trading losses.
“This has resulted in management appointing us as administrators in the early hours of this morning.
“While this timing is unusual in insolvency situations, it was necessary for the appointment to be made once all Monarch aircraft were on the ground.
“This only occurs in the early hours of each morning.
“Once the company entered insolvency, the air operating certificate it needs to be able to fly was effectively suspended, which is why all outbound flights were cancelled with immediate effect.”
Together, the group offered airline capacity of over six million sector seats and tour operator passenger volumes of over 200,000 per year.
The group was headquartered in Luton.
The airline and tour group employ approximately 2,100 people between them.
The CAA has set up a dedicated website, which is the best source of advice and information for affected customers, and a 24-hour helpline for passengers.
It can be reached on 0300 303 2800 from in the UK and Ireland, and +44 1753 330330 from overseas to provide additional assistance.