Boslandew,
I regret that I don't have the actual figures to hand these days and I am not going to try to guess at this late stage as I have been away from the NI operational theatre for some years. No doubt there is someone on the thread who could provide them; these figures might already have been quoted on here already in the past.
However the SH limits cloud and visibility were /are certainly considerably lower than your latter figures for civilian VFR flights. We were authorised to fly under power lines where necessary and used to do so quite routinely. Students were taught this procedure on the OCUs as a basic and essential skill; I recall the minimum limits for that procedure were 6/3/2 metres. That's six metres clearance above the aircraft, 3 metres laterally from the pylon and 2 metres agl, which should give you some idea of the sort of conditions we were expected to fly in, bearing in mind that one reason for not flying over a 200ft pylon could be a very low cloudbase.