If the premise license specifies certain time limits for an activity and these are exceeded, then the Council licensing officers can take enforcement action, including the withdrawal of the licence.

Environmental Health would also no doubt have a view about a level of noise that caused a nuisance in the small hours.

I think you need to contact the Council's licensing department to establish the facts about the license and ask for monitoring to be undertaken.

Also, it's worthwhile for those affected to keep a diary in which to list the date and times of anything which is perceived to be a nuisance. This information can be presented in evidence at a hearing.

It's also worth talking to the police. They haven't been the licensing authority for many years, but they do have rights of audience at licensing hearings and their views are routinely sought.