We have a 2m fence separating our garden from our neighbour's. Just outside our back door, we have a raised patio with a small wall. The small wall is waist height from the patio, and 120cm high when measured from ground level. We have attached a 185cm high trellis to this wall and planted some climbing plants in pots on the patio. So it's quite a high structure altogether. We didn't think it would be a problem as this small wall is at the side of the house (further enclosing the side return, 130cm from the fence). It's well within our property, not on the boundary.
I know that the golden rule with these things is to speak to the neighbours first, but we didn't because the reason we put the trellis up in the first place was because our neighbour has taken to sitting on a sun lounger on top of his outbuilding, directly overlooking our garden, and we wanted to have a bit more privacy. He strips off down to some worryingly loose shorts and positions the sun lounger so he is looking directly into our garden. Our children have found it intimidating, and so do I.
I don't think that the trellis affects the neighbours at all. It might eventually block some sunlight to the top of their outhouse roof, once the plants have become well-established - probably give dappled light, rather than block the light. But it doesn't overlook any useable part of their garden.
Anyway, we had a visit from the planning department and the workman who saw them (I was out) said that someone had made a complaint about the trellis height.
I know that the maximum height for a wall or fence that isn't on the public highway is 2m, but I didn't think this would be the case for a structure that is within our garden rather than on the boundary. We can always cut off the top of the trellis to the required height, if necessary, but would like to keep as much height as possible.
Are trees covered then? Neighbour has large overhanging trees, I'm not bothered too much but they do block a bit of of sun from our garden. Grrrrrr, sorry to hijack and this has probably been asked a million times.
If trees and plants aren't covered then you could replace the trellis with a large acer palmatum in a container (gorgeous) and some bamboo, some species can grow very tall.