I'd like to know what was the likely cause of this fire, whether it was due to gas on a hot engine or turbo, smoking around avgas, electrical faults or whatever, not to judge someone, but to learn from it so I don't make the same mistakes.
It would seem highly likely that it was none of the above otherwise the AAIB would get involved.
Nor would it be likely to be volatile liquids stored in an aircraft otherwise the AAIB would advise against such practice in their subsequent recomendations. If it was a liquid used in the operation or maintenance of aircraft it would definitely come within their remit and demand investigation.