No doubt, but I don't mind it when it isn't overhanging too badly -
it is pretty, and insects like it. I'd prefer not to fell the whole
thing.


Fair comment!

I suppose I could cut it back abit and let the cuttings fall into the
wilderness where of course, it being over a barbwire fence six foot
tall I can't possibly retrieve the bits ("Oh dear - how did that
happen ?") ...

Sounds a good idea since you are leaglly obliged to return them the owner
cannot complain. Have you thought of fencing off the land yourself and
waiting 12 years to claim it by adversae possession?