Thomson Holidays had been doing short breaks and Tours to Soviet Russia and had chartered Aeroflot to fly for them from LGW to Moscow and Leningrad. TU and IL types.
They were very popular and were seen as an exotic getaway.
Finally Britannia Airways (with B737) was granted permission to fly the first ever UK charter flights for package tourists to Russia.
The local ground handling was very 'stern' and strict as one can imagine at those times.
Soviet owned Intourist Holidays also provided packages from London and other UK airports using Aeroflot charters.