The first thing you need to do is call your local police and let them aware of the problem. You can find your local police contact here. If the problem is noise related, you need to contact your local council.

Its important that you keep a record of the behaviour, e.g when, where who, what's happening. Once police think you have got enough evidence, they will be able to take legal action depending on the severity of the problem. For more, you can check UK diregov's site.