Ok, let's not get over excited here, and turn this into a personal squabble.
From what's been said already, it seems likely that this was an organised event, and it seems unlikely that anyone would perform an aerobatic routine, at an organised event, in an aircraft not approved for aerobatics. or without a Permit to Fly. (According to GINFO, there are no Isaacs Spitfires with a valid Permit currently on the UK Register)
I would suggest that the most plausible explanation, therefore, is that this was, in fact, a
real Spitfire, and the sound of it's engine was, perhaps, distorted by the wind, or terrain. This should be easilly verified by a call to the phone number in the Notam.
Although I appreciate your concern DL, regarding what at least at a distance, appeared to you to be reckless/carless flying, I feel that a call to the nearest Airfield to voice your concern would have served your 'word in the ear' purpose better than an expose on PPRuNe.
MJ
