Boundaries always seem to cause problems but to be honest he can cut down what he likes that overhangs his garden but if the tress or bushes grow from your side they are ultimately yours. Surely you/he can take all the clippings to a recycling centre for cheaper than £100 which seems a total rip off as whoever does it will probably use a chipper to get it to manageable size, at least that happens here. Tree surgeons are expensive if you want a tree removed or large branches taken off though.
Our problem came a couple of years ago at a house we rent out when a fence panel came down into our garden from next door caused by her overgrown bamboo. She claimed despite an expensive car and things she was very hard up and could not afford a fence panel even though she agreed it was her responsibility and anyway it was our tenants had obviously pulled it down!!! Over a cup of tea we calmly explained about the bamboo and offered to sever the roots to help a bit and if she paid for the panel( I think one like the one down was £10 from Wickes where we had to go anyway) we would put it up for her, and if she felt the tenants were a problem again could she ring us. All sweetness and light from then on and she let us put it up . A year later we changed tenants when the previous ones moved out and her whole fence was replaced and brand new and far more substantial, so small steps and try and work with the problem.
Briefing against women ministers in Westminster
Walking sticks in "tottery" in old age
What’s a household item that reminds you of your grandma’s house?
