PrivtPilotRadarTech,
It is permissible to commence an aerobatic manoeuvre from what is technically a 'flypast' from the minimum DA height for flypasts so long as the manoeuvre is not technically 'aerobatic' until passing the DA aerobatic minimum. Therefore, pulling up for a looping manoeuvre from straight and level at 200 ft agl would have been within the regulations so long as the pitch attitude was such that it would not have been considered 'aerobatic' before climbing through 500 ft agl. There are many definitions of what constitutes an aerobatic manoeuvre but in general 60 deg of pitch is probably the most restrictive. Therefore, in the case of the Shoreham accident the 200 ft agl entry height was above the pilot's flypast minimum so the relevant detail is what was the pitch attitude on climbing through 500 ft agl?
Although not relevant to this discussion, the same applies on recovering from looping manoeuvres. CAP 403 states "Descent below the approved aerobatic display height to the approved fly-by height is permitted once certain of capturing the aerobatic display height".
Please note that my comments above are based on being a current DAE for class G aircraft which includes the Hunter. If you require any further details regarding these aspects I suggest that you read CAP 403.