Thanks guys for all the fascinating answers...the rotary world is indeed a different one to fixed-wing.
Couple of questions still occur to me though:
1. Whether routing into Battersea or not, when cloudbase is of order of 700'AGL or less, with the right aircraft and licence, does this mean you can fly through the Heathrow zone IMC? So, the SVFR is just a convenience (as for fixed-wing) when conditions permit....
2. Does the concept of "infringement" off a heli-route exist? Or is the fact you're talking to Heathrow Special negate this possibility? I've never seen any stats for heli-route infringements as such....
PS. Yes, took a R22 trial lession afew years back in Jo'burg (much cheaper than UK!) and decided it would be a very bad to ever step foot in a chopper again, as I would bankrupt myself....it was waaayyy too much fun. When you get back in a C152 you sort of wonder why the wings are not doing anything....
BFA