Well the assertion is based on the fact that this fit on this particular Mk of Seaking was never properly trialled and tested in accordance with UK Military Airworthiness Regulations, but that HISL's were merely swapped for the old anti-collision lights. As to "local", I assume you mean those units alone that operated that particular Mk. If so, why do you think that those who operated that type which had not been properly trialled would find it necessary to switch off their forward HISL's in those conditions while other units that operated other Mks did not? I also understand that the BoI conducted its own ad hoc trials to check out these same HISLs and found them to be deficient. Top marks for them, null points for the MOD!
I could make some smart alec remark about your insinuation as to my motives and supposed vested interests but I'll simply say that my sole vested interest is simply to stop the needless waste of avoidable accidents and hence tragic loss of life. It seems to me that the vested interests are to be found in those that defend the existing patently deficient system.