Very Very sad.
Trouble is, even with all the relevant radar services in place, close encounters of the wrong kind can still happen.
I still have very vivid memories of looking at a Dan Air BAC1-11 over Midhurst VOR whilst doing IMC training, over 15 years ago, and it was close enough to be able to see rivet lines down the side!
We were flying beacon hold exercises, just under the TMA at 2400 Ft, with a full radar service from Dunsfold, and suddenly got a call "late call - be aware of opposite direction traffic". We looked, and there it was, fortunately turning away from us, but it was way too close for comfort.
The instructor had a chat by land line with the Dunsfold controller when we returned to Shoreham, and to his credit, the controller filed it as an incident, and it eventually transpired that the problem was the controller at Gatwick. The 1-11 was positioning back to LGW from Lasham, and being worked by Gatwick. Trouble was, the Gatwick controller had suppressed all non Gatwick transponder returns, so he didn't even see us on his screen, so allowed the 1-11 to operate on the base of the TMA visually!
Hopefully, all concerned learnt from that experience, and it's not happened again, as it was a serious pucker moment for us!
I've also had a couple of other close encounters in the SE of England, and yes, some of it is the way that things are so cramped, and some of it is people that won't work within the system, like the Belgian Cherokee that went through the Lydd ILS pattern at 1500 Ft without talking to Lydd, so we missed him by about 300 Ft as he popped out of a cloud in front of us, and then went back into another one. We had been warned that he was sort of in the area, but not communicating with Lydd, the cross channel controller had called Lydd when he saw where he was going, and the height he was at.
At least that pilot did get his ear bent when he landed shortly after in one of the closer to London airfields.
I'm not sure there's an easy answer to this, VFR means Visual, and to really keep an eye on what's out there is sometimes much more easily said than done.
A sad day all round.