Your only real course of action is to have a word with the owners/operators. If you can't see the registration (which does indicate that height is sufficient), then you could try to identify the type - that would narrow it down. However, please bear in mind that there isn't a great deal of open airspace in Surrey. You wouldn't happen to live South West of Battersea would you?
If the reg is on the side, and the heli is directly overhead, you cannot see the reg irrespective of height. This is one of the annoyances.
I do live South West of Battersea, outside the London Control Zone (LCZ).
I am trying to have a word with the operators, but with the difficulties in getting the reg numbers, and the sheer number and speed of the helis it is proving difficult, time consuming and frustrating to make contact. I had thought of getting a radio and transmitting a polite plea to the pilots as they pass
