Strictly speaking, FFF, the radar service IS available in the UK but is provided only to IFR traffic on full-airways flight plans.
In Europe, the UK is relatively unique in this absolutely strict demarcation. If a VFR pilot calls up London Control they will tell him to b*gger off. Whereas outside the UK, if you do a VFR flight at some reasonable level, not in the gutter like most UK GA flies but at say FL055-FL195 depending on the location and terrain etc, you can easily get an excellent service from their equivalent, e.g. Paris Control, Barcelona Control, Brussells Approach, etc and they give you a full RIS, switching you to vectors if they need to. You can do this in the busiest airspace around, which makes a bit of a mockery of the excuses made in the UK. A very refreshing experience. Just got to keep out of Class A
I suppose the UK two-level system has evolved as a result of the copious low level Class A, a general reluctance to permit Class D transits, a resulting training emphasis to avoid CAS like the plague, and the result is that most GA flies down in the gutter where a radar service could not be usefully provided anyway at any reasonable cost, due to range issues.
It's no good asking for pan-UK LARS while "everybody" is taught to fly below 2400ft, or indeed has no choice because of all the Class A.
France nowadays manages a pretty well universal radar service, rather low-key ("radar contact" means they have you on the screen, and you are also cleared for transit of whatever airspace you are about to fly into) but this is for VFR flights at say FL075; you won't get it when working your way through the mass of low level military airspace at 1400ft.
I am happy with the UK system. Statistically based on mid-airs, there is no argument for a universal RIS, notwithstanding the warm feeling it gives you in your heart.
The USA has mandatory Mode C transponders in all the right places - something else which makes an RIS useless much of the time.