I saw one of these objects over the rooftops here a few years ago. I took a photograph and it was published in the paper without comment. The digital camera file has been lost. I recall some men came to my home and ordered me to delete it.

 

 

The one I saw over Merton Park was like that. However I was ridiculed and given psychiatric treatment.

 

The downward facing rim is a reflector to microwaves that come from the engine near the middle. This radio energy keeps it up in the air. It is not strong enough to ionise the air but may be visible as a red glow at night.

Chris