Taxi behind a 747??? In a helicopter??? Dont you folks have a helipad/heliport operation.
I guess its the U.K., just live with it, but its much simpler when Helicopters and Airplanes dont mix. I work out of LAS which is Class B airspace and we never seem to have problems. Sounds like you folks have to have a sitdown with your ATC....
Good Luck, as an SLF at LHR, I know just the fixed wing side is so busy Im guaranteed a couple turns in the idiot circle every time I travel through there.