Sorry it's happenned mate,nothing worse than wanky neighbours.my old girls neighbour and the guy next door down are having problems funnily enough with hedge/border issues.her neighbour found his little daughters rabbit cage open with the rabbit gone,they've laid a new garden but he's on a water meter so my mother offered to let him use the tap by the swimming pool to wet it overnight.my mother could hear banging in the night and noticed the door to the conservatory over the pool was not shut properly.went up to look and the tap had been turned off and the doors a bit dodgy to close so he'd obviously panicked and come out the other door instead which you can't close from the outside.it's not like they live in a shit area either,there's just wankers about.going back to your problem,if he's using the downstairs room as a bedroom then that makes it a HMO or house of multiple occupancy which brings up a massive amount of regulations,sink in each room,fire doors etc etc so you could really stuff him there.