On 29 August, an Antonov AN225 “Mriya” landed at Brize Norton at 20:37 (UTC +1) after overflying Rotterdam, Colchester London and Cirencester. Brize Norton is a military base of the Royal Air Force.
On 30 August at 06:00 (UTC +1), the aircraft is scheduled for a flight towards Athens, most likely the airline will overfly Belgium (thanks Martyn Benson for the tip), as the airline isn’t really flying according to schedule Aviation24.be opened a dedicated forum topic where you can follow the flight schedule.
Follow the aircraft on Flightradar24: https://www.flightradar24.com/data/aircraft/ur-82060
You can see a remarkable recent picture of this unique aircraft by one of our members in our Contrail Spotting forum: https://www.aviation24.be/forums/viewtopic.php?f=25&t=64097&p=371666#p371664

AN225 landed at Brize at 8.37 pm local time this evening after overflying Rotterdam, Colchester London and Cirencester.
Taking off at 06.00 UK local on Thursday morning to Athens and likely to overfly Belgium
Thanks for the information Martyn!