Exceedingly loud helicopters seem to regularly fly in the sky where I live in the London Borough of Islington, both in the day and night, and often on Sundays, when noise is supposed to even be legally restricted in the day. What methods are available for one to find out who these helicopters belong to, and what they’re doing? Further, what recourse do disturbed local residents have to complain or prevent these helicopters from so severely disturbing them?
The U.K. Civil Aviation Authority provides information about making noise complaints to the relevant airport. It also notes that your local planning authority can provide more information about operating hours and noise restrictions. You could also ask at Aviation Stack Exchange for more information about identifying the aircraft and owner.
This is also a political issue that Parliament attends to from time to time, so you can talk to your MP about it:
At common-law, there might have been causes of action available in trespass, nuisance, or public nuisance, but the Civil Aviation Act 1982 says that "[n]o action shall lie in respect of trespass or in respect of nuisance" as long as aviation regulations and orders are complied with.