The you tube interview with Taffy Holden, cited earlier, includes the following
Although the tests I did and the ensuing flight did not immediately provide a reason for the initial electrical fault, my electrical staff, with additional assistance from English Electric, Salmesbury eventually did. Apparently, in early versions of the Lightning, there was to be a ground test button fitted into the standby inverter circuit. It was never fitted to the Mk1A but the wires were left in the looms. It was one of these redundant wires which shorted on to the UHF radio as it moved on its trunnions when the aircraft nudged forward on take off. Who would have thought I should risk my life to find it, in the way I did?"
