Lj101,
Unfortunately I think that you are a little out of date with some of your 1 Gp Rules. "Sufficient visibility for the aircraft to be kept straight without reference to instruments" is definately not acceptable to those who fly civilian registered ac in the RAF.I believefor them a minimum RVR or Met Vis is required for takeoff. I used to laugh in the last days of the Dominie at Cranwell when being told by some youth (Tutor QFI) that "you can't go flying in that weather, the vis is only 300 meters". To which the answer was "of couse I can, it's legal and in my opinion safe"
I believe that soon all Brit Military ac will soon have to comply with civilian regulations. Best get a current IRE to answer. The RAF will loose some of it's operational capability by giving way to these risk adverse people who do not properly understand Military Operations.