The height makes no difference. If it is safe when SVFR then it would be safe IFR provided that the flight was below 3000ft clear of cloud and in sight of the surface.
For example, in ideal conditions (sufficient manning and reasonable workload) ATC request just 3 minutes notice by R/T before zone entry in order to issue a clearance. It is often totally impractical for a helicopter pilot to put in a written flight plan because of the type of ops involved (e.g. no facilities and no-notice changes to the task) so this is of huge benefit.
Perhaps you have not realised it but your "ATC request" is in fact filing a flight plan. Perhaps the 3 minutes notice would be a bit short (10 minutes is quoted in the AIP) but having to hold for 7 minutes when you know you are going to get in is better than simply a "SVFR not available" message.
Under IFR this would not be allowed, standard separation would be required
Standard separation is required under SVFR also. Not to mention that in Class A airspace and Class B airspace, all flights are provided with separation be they IFR, VFR or Special VFR.
If you are happy to give away your right to separation against an opposite direction traffic in 6Km SVFR then if you are IFR in the exact same weather, other than having certain rules to follow, where is the difference in safety standards?
Yes it would make Battersea a bit more quiet and would mean that only the better equipped and crewed heli's can make it through but it would keep the system operating for those people who made the investment in crew and equipment.
Regards,
DFC