Timbo.
I have an answer for you!!
We had this problem....and solved it.
We arranged to spend the night away from home.
I borrowed a Yamaha organ from our friends, and set it up against the lounge wall seperating our semi from our obnoxious neighbour who often partied until 4am.
I set up the organ to play a very untuneful sequence with lots of horns, cymbals, drums, whistles, jet noises and other irritating sounds. Put it on a long loop, and TURNED THE VOLUME UP TO FULL!!
Then we left for the night.
He came round the next day, furious, and full of wind and threats, and I told him that unless he kept HIS noise down, we would be repeating the operation and that I might even BUY the organ!!
Shame...He and his wife never got any sleep that night!! But he's not had any parties since.......and that was 4 years ago!!