I've been flying in that local area for 30yrs, most of that instructing and some out of Wycombe.
It is very busy airspace but sadly anyone who has been flying long enough has had the odd near miss, this is just a tragic accident.
Getting in my car and driving around the M25 is far more risky.
Forcing GA with compulsory TCAS sort of gadgets will not solve the problem - It will just pander to the 'gadget brigade' who never look out enough, and won't show up the non squawking traffic.
My condolences go out to those involved in this sad accident. RIP.