Peter - I do agree wholeheartedly with your comments.
There are 2 main problems with going under HT wires - the first is the risk of disorientation if you look up to check your clearances, this should have been established before you venture under them by comparing the height of the cables with the rad alt reading (if you have one, if not you are just cuffing it).
The second problem is that of arcing - when I told a relative who works for National Grid, he was horrified that we taught people to hover taxi under HT cables. The guys that work on them (not in helicopters) have to comply with stringent safety precautions - 400KVA is a sh*tload of power and, whilst you might hope that any arcing would be routed around the helicopter by the bonding of components, it wouldn't take much to get that wrong.
Pick another LS!
The thread running on 'Helicopter down near Tring' seems to indicate yet another unplanned coming together of HT cables and helicopter!