Holidays, including flight-only and accommodation-only bookings to Los Cabos, Mexico, and Kvarner Bay, Croatia, departing on or before October 31, are also cancelled.
The tour operator has stopped issuing credit notes and is instead offering cash refunds to all customers impacted by cancellations.
However, customers who were previously given a voucher have until the end of September 2021 to book their holiday.
In their latest update, issued last week, TUI said: “We’re aware of the media reports regarding international travel not being able to take place before July 2021.
“We would like to reassure customers that we still expect to understand more about international travel on the 12th April from the Prime Minister, with the 17th May as the earliest day for travel.
“We will continue to update customers when we know more information. We know our customers are looking forward to their holidays, so to offer continued flexibility and reassurance, we have extended our free changes policy to the end of June.
“Those due to travel between 17 May and the end of June can change their booking to a later date fee-free through Manage My Booking, or if you’ve booked in a TUI store by calling us on 0203 4512688.”
TUI has cancelled all flights and holidays until May 16.