I think Britannia started off in a hangar built by Luton Corporation who built it to attract an airline to the airport. Around 1970 they moved into their newly built hangar 89 next to the terminal. Court Line then moved into their old hangar to maintain the Tristar's.
At some point while keeping hangar 89, which was too small for the 757 and 767, they moved back into hangar 65 which was rebuilt.
Years later Easyjet moved into hangar 89 leaving leaving Britannia with just hangar 65.
Nice photo here taken by RA Scholefield which appears on airliners.net outside the then Courtline hangar.
Photos: Bristol 175 Britannia 308F Aircraft Pictures | Airliners.net