Before anything else, I offer my condolences to those who lost their lives (or their loved ones and friends) in this accident.
Whilst we will have to wait for the outcome of the investigation to know how this happened, there have been many comments out airspace classes and flight rules, many of which appear either incorrect or based on misunderstanding. As I understand the situation, both aircraft were in communication with Coventry ATC.
Although airspace class and flight rules are not entirely irrelevant, there is a very grey area over what ATC has responsibility for in the vicinity of an aerodrome, and particularly the aerodrome controller's responsibilities for managing an orderly flow of air traffic. Make no mistake, the aerodrome controller's job in an environment like Coventry is not easy - whether issues of airspace, flight rules or IFR/commercial flight outside CAS etc. are particularly relevant will no doubt become clearer from the investigation, but if it results in the clarification the grey area of aerodrome control responsibilities it will be no bad thing - for pilots and controllers alike.