To ask my new neighbours to...

[MrsWhirling]

...remove the bright green washing line they have tied to my tree, in my garden (to create their own washing line)? They didn't even ask me. I feel a bit miffed.

Also by taking the pole round, I'd interpret it as being you are ok with the line and are encouraging them to use it

Wait until they have washing out then cut the line.

Definitely take it down now.

Is there a fence? I'd just untie it and place it on their side.

Tying to a fence would really annoy me - fences aren't designed to have a heavy load of washing pulling from the top of a pole, and it could easily cause issues (although if its their fence then that's their business)

The tree, well, I think it's a bit cheeky, and if you don't like it, then untie it. They can just do what anyone else who wants a washing line does, and find something of their own to attach to/use a rotary dryer. If it's left there then it'll start biting into the tree and cause a wound.

Just say you would rather they didn't use the tree.