The only time I lost a Derwent inadvertently (which is different from a "failure") was during a visit to 208 (FR) squadron by the CFS "Trappers". Although I held an A2 Cat on type, I was not being employed as a QFI but as a Flight Commander. Yet the trapper I flew with insisted on playng one-upmanship. I think he had a background on "heavies" and wanted to show us "steelies" that he could do anything we could do, only better. So he made me "patter" the spinning sequence although I reminded him I was not a squadron QFI. All went as per text book - boring! He then asked whether I had tried an inverted spin; I pointed out that the manoeuvre was prohibted in AMFOs and in the Pilots Notes (I think). His attitude was that such pettifogging restrictions did not apply to Aces from CFS Examining Wing. I had signed the 700 as Captain (although I was a Flt Lt and he a Wg Cdr) and I regret that I weakened and let him talk me through a normal spin and a recovery during which the pole was held hard against the instrument panel after the spinning had stopped. Brutal, deliberate mishandling. The aircraft faffed and juddered around a bit and then entered a quite gentle inverted spin, recogniseable only by the quite high nose position and some tolerable negative 'g'. He then told me to recover and I centralised the rudder and started to move the stick firmly and progressively back. All hell broke loose! The negative 'g' and I hit the roof, IAS started to build up rapidly and I started to "red out". There was a strangled grunt of "I have control" and some seconds later I recovered consciousness. We were well below 5,000 ft and one engine was out. Presumably the inverted spiral (for that was what we had got into ) had exhausted the negative 'g' trap in the fuel system. A few more seconds and we would have lost both engines. Well my stock of "the Right Stuff" was limited (I was never test pilot material) so I was a bit shaken and bloody angry. I relit the engine and we flew back to Abu Sueir in a strained silence. On landing I loudly called for Chiefy and grounded the aircraft for a stress check (the accelerometer was showing some horrendous figure). THe aircraft (almost brand new) was bent, but acceptable by MEAF standards. It never flew nicely again. God save us all from "experts".