Ickenham Travel Group has lost its ATOL licence, the Civil Aviation Authority said.
The London travel firm ceased trading as an ATOL holder last week.
It has been trading under several brands, including Abu Dhabi Holidays, Ras Al Khaimah Holidays, Letsgo2.
It operates several web sites including RasAlKhaimahHolidays.com, abudhabiholidays.co.uk, and justallinclusive.com.
The company originally founded as a single travel agency store more than 50 years ago.
The CAA says for customers currently in destination, the return flights are valid and they should check in as normal for their return home.
For other booked customers, it said: “If you have an ATOL flight inclusive package booking and have been issued with flight tickets, the flights may be valid for travel, and you are advised to check with the airline.”
“If the airline confirms you have a valid ticket for travel, you may have the option to travel.”
“However, other services may not have been paid to the local suppliers, and you will be required to re-arrange and pay for these services again.”
The CAA advises customers to check if other services have been paid and confirmed before commencing their travel.
“To avoid any issues in resort, you should confirm the cost of all the services in advance of travel where possible.”
