LRRP,
I gave you a list of the most appropriate Units in the Essex/Kent/Sussex area, so if you know where you are you should now know who you might contact/listen to.
I THINK I understand your last paragraph.... A7000 is a conspicuity code - it indicates to a controller that you are operating outside controlled airspace and not receiving a radar service. It also assists controllers in actually seeing you on radar, as primary radar cover at low levels can sometimes be less than optimal. I would always recommend you squawk altimeter (mode C). This will allow Thames Radar to warn IFR flights at or descending to 3000ft of your presence, and perhaps pre-empt TCAS episodes. Of course we can take no action if we see two A7000 squawks converging, BUT you are supposed to be operating under visual flight rules i.e., see and be seen. Even when receiving a radar service you should not be lulled into a false sense of security and relax your lookout. There are a myriad of reasons why a controller might not be able to call traffic to you.