From
https://monarch.caa.co.uk/:
Monarch Airlines has ceased trading
Information for customers of Monarch
Monarch has confirmed that the following companies have ceased trading and now entered administration:
Monarch Airlines Ltd
Monarch Holidays Ltd (ATOL Number 2275)
First Aviation Ltd (ATOL Number 4888) previously trading as Monarch Airlines
Avro Ltd (ATOL Number 1939)
Somewhere2stay Ltd
As a result, we are sorry to inform you that, as of 2 October 2017, all future holidays and flights provided by these companies have been cancelled and are no longer operating.
This is an unprecedented situation and because there are up to 110,000 passengers abroad, the UK Government has asked the CAA to coordinate flights back to the UK for all Monarch customers currently overseas. These new flights will be at no extra cost to you.
If you are already abroad you will find all the information you need about your new flight on this website.
If you are due to depart from a UK airport with Monarch Airlines today or in the future, please do not travel to your UK airport as your flight will not be operating.
Customers already abroad
If you are currently abroad and due to return to the UK on or before 15 October 2017 we are making arrangements for you to return home to the UK on a new flight, at the end of your holiday. These new flights will be at no extra cost to you.
We will of course prioritise vulnerable passengers, including unaccompanied minors, and make sure that family groups travel on the same flights.
For further advice and details of your new flight please read I am currently abroad.
If you are currently abroad and due to return to the UK after this date, please read the additional information section.
Customers yet to travel out of the UK
We are sorry to inform you that all future holidays and flights booked with Monarch are now cancelled as of 2 October 2017.
If you are booked on a Monarch Airlines flight, please do not go to your UK airport, as your flight will not be operating.
Further information is available at I have a future booking and have not travellled yet.