<<Swanwick has a major training facility, virtually next door to the main site that can be switched to take control of the live environment. If that was deemed appropriate, I'm sure they would have done so.>>
But where do you get the staff to man it in an emergency? When I moved from Heathrow to West Drayton with the Heathrow Approach sector, staffing was arranged so that both units were manned until after the move had been proved successful. When something breaks down you can't simply magic-up a whole ATC watch!