To avoid wasting time and fuel or waiting for a diverse crossing of airspace being granted, it is preferable to plan for a standard route through preferred airways crossing routes.
The Lichfield Corridor was realigned many years ago to accommodate the needs of TACAN-only fast jets. It became a direct track between the Coningsby and Brawdy TACANs. It used to be higher, but was lowered to avoid conflict with airways traffic inbound to Manchester. It has since been lowered yet further and the normal entry and exit waypoint locations appear to have been tweaked to suit Voyager's turn rate.
Of course when Q calls, I imagine that 'Air Defence Priority' is still available?