Uncle Ian, your comment about VFR not needing any control is sadly way off the mark. You would be surprised how much extra work VFR traffic creates on a sector.
Personally, I think that a NSF is a waste of time: People off other airfields south of Heathrow route H7-H4 rarely phone up to activate or quote an NSF. Maybe we should give all of the helicopters wanting to be on H4 at the same time a slot time +/-5 minutes......