First of all my sympathies go out to the families and friends of the victims of this tragic accident.
Having spent many an hour jammed between Luton and London and squashed down by the TMA above, I am not surprised this has happened. It was only a matter of time before something like this or more tragic happened. I have personnally witnessed a couple of prats doing aeros close the one of the entry points to Luton's VFR lane, in another instance, a pilot hidden deep in thought behind a charts. It never ceases to amaze me what poor airmanship some people demonstrate.
It is an extremely busy bit of airspace, with a huge variety of aircraft, from microlites to private jets. Only goes to show the importance of a proper look out and good airmanship.
Safe flying everyone.