The Hunter also had a means to isolate the twin HP fuel pumps to maintain a fuel flow in the event of HP pump failure. This was activated by a guarded switch in the cockpit behind the throttle. This High Pressure Pump Isolation Switch (HPPIS) could result in a considerable over-fuelling of the engine, the consequences of which would be an almost instant over temp/destruction of the turbine.
In the interests of accuracy, this system was fitted to the 100-series Avon (and thus relevant to G-HHUN and the Shoreham T7) but was not on the 200-series as used on the F6 and its derivatives.