Not every problem has a solution, and this one doesn't have one.
All the time it is permitted to navigate using such error-prone means (and I am not saying it should not be permitted) and all the time PPL training is just basic like it is, and all the time there are so many low-time pilots, people will be getting lost.
A radar service will pick up only those who are on frequency and are readily identifiable (with a transponder). One would need mandatory radio contact in Class G and I think that would be a shame. I would much rather have mandatory Mode C than mandatory radio contact.
Farnborough was very busy today - doing a great job as ever but as busy as they could handle I suspect. There is no way they would be able to handle mandatory radio in their radar area - they would need several controllers instead of one. This is another reason we don't have decent ATS for Class G - the workload would be huge and the services we do have hang in there only because many/most pilots fly non-radio or with a listening watch only. London Info need everybody to call them up like they need a hole in the head.
Mandatory radio contact exists in the IFR (airways) business and it works there because people are (generally) navigating with total accuracy and can be left alone for hundreds of miles until they need to be shoved around for a particular reason. But to eliminate CAS busts using a radar service would mean micro-managing loads of targets, many zig-zagging around like ants. It's plain silly IMHO to suggest that a radar service is a solution.
One could virtually eliminate CAS busts but it would involve a total transformation of GA practices: making everybody fly preplanned routes, no bimbling around, and everybody radio-navigating as per IFR. That's how I fly when I go somewhere for a purpose, and when I deviate from the planned route it is done with the utmost caution and with the aid of the CAA VFR chart running as a second GPS moving map. One cannot seriously suggest that everybody should be doing that, but it's probably the only way to make a dent in the problem.
If one wants to bimble around randomly OCAS, and obviously I believe the right should be preserved (remember it isn't a basic human right - a lot of Europe doesn't have it; try doing your own thing, non-radio, in say Greece) then mistakes will be made by a certain number of people. Dead reckoning is no good for random track navigation; sticking to well known local area is one way, a decent GPS is the other way but there is no way to push that one through. No normal aviation GPS is any good IMHO (not even the Garmin 496) because their airspace depictions are confusing as hell.
30 years from now, when nearly all spamcans will have huge glass panels, people will wonder what the fuss was about. However I think pilots' right will be seriously curtailed by then in other departments.
Now, all those old navigators will jump on me. Just remember that not every fresh PPL is an ex RAF 10,000hr expert sextant operator, or a special forces pilot, or somebody who knows the local area intimately.