A similar trick was played on pilots 'guesting' in the Hunter 7. The hydroboosters were turned off 'in order to hand control to the other pilot'...
Re. the Tin Triangle, it didn't have hydraulically powered flight controls. Just mechanically signalled electrically powered Boulton Paul PFCUs, much like the VC10. Hydraulics only powered the bomb doors, undercarrage retraction system, wheelbrakes, nosewheel steering and AAPP intake scoop. Unlike Fred's crecent winged thing, it had no flaps/slats to worry about, the airbrakes were driven by big 3-ph AC motors and all PFCUs, autostabs and feel were powered from 4 independent AC busbars.
I can't recall whether the H2S antenna was electrically or hydraulically powered.