Anyone know who to complain to about this? Does it work? I'd love it to stop or at least cut down, or at least to come with some kind of explanation backed up with facts.
If you want to complain and you know it's the police helicopter I would suggest you write to the Commissioner at New Scotland Yard or the Chief Superintendent in charge of Haringery Borough Division (based at Tottenham Police Station I think - check the Met website).
You have a valid issue and you are not alone in raising it. However, you should note the following:
1. It's nothing to do with the helipad being at Lippitts Hill that you get any more - they only have a couple of bases from which they cover the whole of London.
2. They only get deployed to incidents where they can add some value, not just because they've nothing better to do. These include vehicle pursuits (way safer with them involved), searching for missing vulnerable people (can cover far bigger areas far quicker), searching for suspects for serious crime being chased on foot or who have hidden (have heat seeking camera equipment and maximise chances of capture quickly and safely).
3. In all the above cases they may be below normal height and they may be over the same area circling or hovering for some time (though rarely more than 10 or 15 mins). They will always go as soon as the need has gone, but chases and searches do take some time to resolve.
4. They rarely go looking for cannabis factories (by using the fact their roof lights up brightly with the heat escaping!!) specifically - it's more that they scan around during normal flight routines. Even if they do, they do it from normal height and don't hang around (because that would alert the suspects!)
I would suggest you write, drawing attention to the ongoing issue and raising today in particular but, rather than simply complaining, you ask for an explanation and then complain if that doesn't appear or doesn't justify the disturbance to you.
You can also go to your next Community Police Consultative Group meeting (check local council website) and raise the issue (the Chief Superintendent goes there and answers questions).
You can also go to your next ward Neighbourhood Policing Team meeting and raise the issue (they probably won't know though, but may be able to find out).
If you don't know that it was the police helicopter, you could try the Civil Aviation Authority who should be able to identify it from time / date / place. It is highly unlikely to be anything but the police one though - the ambulance one tends to come and go (and you would hear of the incident it was called to locally) and no others have authorisation to be low over London (the river is the route to Battersea heliport and armed services ones have no reason to hang around).