If they're licence is from 1000-2300 but the music starts at 2300 and goes on all night, they're most likely selling alcohol outside of licensed hours too.
If you kick up enough of a stink with the council and police, and I mean sending a letter to EVERYONE every day and several phone calls to EVERYONE every day, they will get fed up with you badgering them and will get off their arses and put a stop to this nuisance, ie do their jobs.
If that still doesn't work you can always play dirty....