BBF,
the classic VFR into IMC accident that claims PPLs every year.
As a PPL who takes considerable interest in such things I can tell you that the "classic VFR into IMC" fatal accidents by PPL's in the UK are caused by inadeqately equipped pilots not qualified to operate in IMC. Hardly a description of Cook and Tapper, although it would appear that "inadequately equipped" might be relevant.
Surely, the benefit of the considerable doubt in this case should be given to the pilots if only on the basis of their experience and qualifications to fly in the prevailing conditions. If you add the doubt about the state of their equipment, the case for a more just verdict is surely made.