Clearly there are many facts not yet available in this particular case, but the general case of mixing IFR and VFR traffic seems to have generated a lot of confusion.
As I understand the ICAO rules -only in Class B and C are VFR and IFR actually separated. In all other classes IFR flights either get traffic information on VFR or nothing.
In most countries, on a VMC day there will be VFR and IFR traffic both using an airport and most countries don't have the VFR traffic orbit for 5 minutes while an IFR approach happens, they slot the traffic together efficiently - just like what probably was happening in Coventry - why it didn't work and what should be done about it awaits the AAIB report.
However, it is concerning that such a volume of people are operating IFR, apparently unaware that the cacooned world of low level Class A and Class D operated like Class B that is the South of England is the exception rather than the norm. In particular, the expectation that being 'IFR' in Class G gives some sort of protected airspace. Although sometimes it feels like we have four types of flight rules (VFR, VFR in IMC, IFR non-airways, IFR airways) - There really are only two and IFR coming off an airway (or cleared on an ILS) may get a different default service from ATC, but to my knowledge it isn't a different set of rules to other IFR flying.
As I understand it in France, Benelux, Germany, Australia, USA, South Africa, etc. VFR traffic can and do operate into most airports and in 'airways airspace' up to roughly 18000 feet intermixed with IFR traffic.
The UK is however clearly unique in the world in having such large amounts of heavily trafficked Class G AND allowing flight in this airspace in IMC without participating in any separation or information service AND providing a Class G separation to participating IFR traffic from SOME other IFR and VFR traffic. To that extent, I think there are some real questions about airspace design and separation service. HOWEVER, this doesn't seem to be relevant to a situation where (on current information) both aircraft were in contact with ATC and both were approaching to land, the conditions were VMC - this could equally have happened in Class D airspace (operated to ICAO standards), and it could have happened regardless of which flight rules the 402 was following (clearly if the 402 was receiving a RAS service he would be separated from everything - but once again a UK unique service)