With respect HD, "ATC in that area" as you put it do not know about every flight taking place, as I said, the area which luigi is referring to is class G where we all know and expect all types of flights to operate at any time of the day or night unknown to any ATSUs.
I doubt movements are taking place after the normal hours at Biggin Hill and I doubt large jets are coming down to 50ft. What these local people are seeing as they crawl out of the The Crown pub at 2am is more likely than not to be one of the 2 or 3 police helicopters chasing stolen cars between (the well known to the poilce ASU) New Addington council estate and Biggin Hill below 500ft as they are entitled to do as they are exempt from the low flying rule. If it is not the police, it might well be the military on a low level night sortie using the VOR (owned and operated by NATS) who are also exempt from some of the ANO or aircraft in the Biggin hold for Heathrow at a level not at all low.
When they say "large jets" I wonder how large they mean?
If the local residents seriously belive that movements are taking place then perhaps Bromley council should review their own CCTV recordings that they are rumored to have installed around the airport to keep track of out of hours movements!
Luigi, when you posted this had you just crawled out of the The Crown?