While our house was empty our neighbour got planning permission to replace his garage. When we got back we discovered that the roof of the new garage overhangs our garden and has trapped the fence so we can’t remove the panels. We complained to the planning department but they say there’s nothing they can do.
The projection of the garage roof over your land is an unreasonable intrusion and will probably be reckoned to be a trespass and actionable in the County Court. This being the case you can ask the owner to take the roof back to the boundary; if the garage was designed by an architect your neighbour may be able to claim damages for negligence. Alternatively you can reach some sort of compromise over the fence and remain on speaking terms with your neighbour.