Wonder if anyone can help me here.

My next door neighbour moved in last year after the previous neighbour
was evicted for various tenancy breaches. Just before the previous
neighbour left, they planted what I can only imagine to be a leylandi
shrub. That was last July, and now the shrub / tree is over 8 foot
tall. Whilst the neighbour is fine, he doesn't want to cut the shrub
(he reckons it looks spectacular!) and it looks like by the end of
this summer it will be dwarfing our 4 foot fence by some considerable
height!

Apart from looking unsightly, the actual shrub / tree (what can you
call it!) is no real problem BUT it's right next to where one of my
washing lines are so any strong winds and the sheets get a good
battering! I've stopped putting the washing there before anyone asks,
but the branches are well and truly growing into my garden. My
question is: without chopping the stem of his shrub, would it be
illegal for me to chop the branches that are growing into my garden?
For a start he wouldn't even notice I'd done this but I wonder if
anything over my fence is "my property" And can anyone guess how tall
this monster is going to grow (and can anyone guess what it might
be?). Fortunately, as it grows taller the actual middle part is
thickening so it's losing it's ability to reach my second washing
line... I do worry about my fence though, will the branches at the
bottom end (ie up to 4 foot) start to push tightly against the fence?

I'd like to actually cut the thing in half but that's a no-go

As I say, it's no real problem, apart from it needs a good cutting but
what about the bits that are now working their way into my garden?

Cheers

Robbie