The only reason you need a twin for power line flying in UK is when you're checking over built up areas. The SWEB unit have been using Twinstars and 206s for over 40-odd years and have only had one accident, and that was only after a flight tester pulled the guts out of the engine. At the levels they fly, you're going to be very close to the ground anyway by the time you recognise an engine failure in a twin.
We had a special low-level engine failure slot in the PPC.
You're more likely to have an inexperienced pilot be blown into wires while in the wrong position downwind than have an engine failure. Then again, the engineers at the SWEB unit are top-notch.
Because of the high inertia blades and its crashworthiness, I think the 206 is the absolute minimum s/e machine to be used on powerlines, especially on those 11kv lines in Wales and Cornwall!
Anyway, the Twinstar is the only twin that is small enough not to annoy the neighbours.
Phil