Normally I think it's always best to try and resolve situations at a low-level. So, start with the neighbour, have a chat etc.
BUT it's a listed property!
Holy Fuck!
That is SUCH a huge no-no to start making major changes like that.
Straight to the council. email them the photos.
I don't know where you live, but this from a .gov page of Arun:
"You may also be liable to prosecution as carrying out unauthorised works to a Listed Building is a criminal offence."
No wonder the builder took his stickers down - this is a criminal offence!