ATCO2,
All traffic in class A are separated.
Even if it was a class E (the lowest level of controlled airspace) control zone, Special VFR flights would be separated from IFR flights.
Thus in this case to meet the requirement that all traffic in Class A is separated, the heli lanes and levels must be deemed separated from the IFR flights.
If that is the case then an IFR flight along the heli lane at the same level would be just as much separated as a SVFR flight.
Remember also that SVFR flights are separated from other SVFR flights also so no difference there also.
As for an IFR procedure at Battersea, none is required since in order to fly the heli lanes IFR the flight would have to be visual i.e. clear of cloud and in sight of the surface. Thus a visual approach would be a viable option.
Note that by being IFR below 3000ft but clear of cloud and in sight of the surface, one can effectively remove the visibility requirement for SVFR (or at least reduce it). Not saying that it would be safe in all cases but those are the rules.
If your next question is what does the IFR flight operating visually do if it can no longer operate visually then the answer is just the same as the SVFR flight......but being IFR equipped and with an IFR rated pilot, the options are better.
The point I was making is that in black and white there is VFR and there is IFR. Pick one to fly by. However to be less restrictive, the CAA has permitted the grey to enter the equation this thing called Special VFR but it is totally at the discretion of ATC.
It is the classification of Heathrow Zone as A ( and Jersey zone also) that really makes SVFR necessary even when it is CAVOK. The airspace category is where the complaint lies. Not with ATC and not with NATS since any ATC provider would act in the same way.
Regards,
DFC