Making a complaint
All neighbour noise problems are best dealt with informally by having a chat with the neighbour concerned, or even a short polite note. Don't assume your neighbours know that they are causing you a problem. If you let them know you are having a problem then at least you give them a chance to sort things out without resorting to the law first! Sometimes there is a need for compromise. But, there are occasions when you don't want to approach a neighbour directly. You have the right to make a complaint about noise nuisance to the local environmental health offices.
Local Authorities have a duty to investigate noise nuisance complaints. Most complaints received by councils relate to domestic noise. The Environmental Protection Act 1990, Sections 79 - 81, defines a STATUTORY noise nuisance as being noise prejudicial to health or a nuisance from premises, and from vehicles, machinery and equipment in the street, and the powers of the local authority to deal with the problem. (Noise also includes vibration).
Remember also that the investigating officer (usually, but not always, a qualified environmental health officer) MUST have enough evidence of his own to build up a good case against your neighbour. Otherwise, how else can the Council take any further action, beyond perhaps a letter informing your neighbour that a complaint has been made and what it's about? You might be asked to keep your own diary of noise nuisance events, but this is not 'evidence'. The information is used by the investigating officer to 'score' the factors above, and decide on the best times to visit if necessary. The officer will assess all this information, and will be sufficiently experienced to know whether this case looks like one which needs further attention or is one which falls into the "ok, you have a problem, but this situation will be unlikely to be a case for statutory noise nuisance action". Without enough quality evidence, the Council is powerless to take any further formal action. However, if the Council has not already sent a letter, there may be enough information to justify an 'informal letter' to the neighbour at this stage. On the other hand, you also have to weigh the possibility that your neighbour will be offended by the fact you have the Council involved, and will the problem only get worse. It is your choice.
Formal action
On the other hand, let's say that your diary records scored highly if one was asked for, and that your complaint has been investigated. The environmental health officer agrees that a statutory noise nuisance exists. What then? The officer then has a duty to serve a 'Statutory Nuisance Abatement Notice' on the person causing the problem if they are known, or the owner of the premises, or both. The Notice will have to specify exactly what the problem is, and what action must be taken to comply with the Notice, and a time scale (usually at least 21 days which allows the recipient opportunity to appeal to the Court against the Notice. If it is an 'emergency' and in the public interest then this can be reduced to hours, for example when dealing with a continuously sounding audible intruder alarm when it is known the occupiers have gone away. In this case the Council will usually take steps to carry out the work after obtaining a warrant of entry from the Court, and recharging the costs to the owners or occupiers of the premises).
Sometimes the action or work required is straight forward, sometimes a bit more difficult. But if the Notice is not complied with within the stated period of time, i.e. the noise problem does not stop, then the Council is obliged to pursue further legal action because at this point the neighbour is guilty of an offence. Again, the Council needs to get more evidence to prove that the nuisance is still happening after the expiry of the Notice. If this evidence is available, then the council will issue a summons on your neighbour to attend court. Your evidence in court may be needed depending on the circumstances.
If the magistrate agrees that your neighbour is guilty of the offence of causing noise nuisance and failing to reasonably comply with a Nuisance Abatement Notice, the fine levied can be anything up to £5000. So if you are a person being accused of a noise nuisance, think carefully about the possible consequences. Courts these days take noise nuisance very seriously, and a first fine of £2000 is not unusual!