I didn't quite know where to put this, but i'll try here first.
The neighbours to the back of us, their back garden backs onto our back garden, have some large tree problems, - well the problems are ours really 
I want to approach them with a letter to ask if they would trim them and wonder if I have any legal leverage or not, I can't find anything in what I've been looking at so far, only what is reasonable to do, but not compulsory.
Firstly is their weeping willow tree; - since we have lived here, over 12 years, it has appeared and grown I would say about 30ft. We only have short gardens so I guess its root system would be near our water drains by now, not that this is an apparent yet but I understand can be a problem. They have never trimmed it or given it a good haircut as I see others around the area do.
Some of it now overhangs our garden by about 12ft, I realise we are able to cut overhanging branches but obviously these are pretty high up and out of reach and we would need to pay for a specialist I would imagine.
The second problem is the row of trees planted by them along the back boundary (about 15ft high). These have over time thickened and grown into the boundary and last year when we replaced the back fences we had to dog leg the run of fences to accommodate them encroaching on our garden . Perhaps this was a mistake and we should have taken charge then, but the owner came out while the work was being done (at our expense I should add) and started filming the fencers at work, so we were a bit intimidated/bullied into losing a few inches of our garden boundary. (I realise how daft that sounds)
A bit of additional info: - I know they are tricky people, certainly regarding trees - last year they stood under the overhanging branches of another neighbour’s tree to prevent them from trimming it.
So, how to approach it.
I would like the willow properly trimmed by half its size.
I would like the growing-over-my-boundary-trees removed but would be satisfied with them kept to 10ft.
Any tips or help on getting at least some of this done so I can reclaim my garden and light would be appreciated.