In reply to gethin_allen:
I have legal training, but I suspect what you need is somebody with *qualifications* in law.
Before you go any further, I'd introduce you to the principles of what people are allowed to do, and what they actually do. The legal profession makes its money off the mismatch between the two, generally with less gain to either of the paying punters involved than to the solicitors under instruction.
Your neighbour has rights under the Party Wall Act to do stuff to the outside of his property, but he's supposed to inform you first and *should* agree the scope and extent of any works. However, your rights of redress are limited to financial loss and, in theory, to compensation for any detriment caused by his actions. I'd suggest a whiff of cooking won't cut much ice in court and any award you got almost certainly wouldn't cover your legal fees.
What can you do? Spend money on a solicitor, who probably won't talk you out of spending said money for the first few hundred quid, but who ought to advise you not to go to court; lamp the neighbour and have ongoing hassles for ever more; have a grown-up word about the fact that he should have talked to you first before coming on to your property and then move on.
Or construct some kind of Heath Robinson contraption which ducts his emissions through a pipe which curls back onto his property. Make sure you don't actually *touch* his stuff, but he couldn't actually argue about it.
Me? I'd have a quiet word about him not having come round beforehand and then wait to see whether it was a problem.