pitch up at the zone boundary requesting a transit, and you're told to remain outside for 10 minutes, just think that the IFR traffic ahead of you could have been sat on the ground for an hour or two, full of passengers, taking their delay without complaint. I know it's easy to look at the snapshot of traffic you hear on the r/t, but take
Squawk 7500, if landing in Class D, I always do, as per the mandatory requirement for the LHR CTR's inner area, which has been carried over from the recently changed Class A days ( I was doing this long before AIC Y049/2011 was published). However, the nature of the job means we cannot always do so ten miles in advance for a transit flight. But we never "pitch up at the zone boundary", we do try very hard to give the required notice; we try to be as helpful and expeditious as possible, knowing that this is mutually beneficial.
As for airline passengers being delayed on the ground, no doubt you are aware of the requirement for operations in the Heathrow CTR for VFR and SVFR traffic to have the "equivalent delay" applied, apparently so even if the GA movement has absolutely no effect on IFR traffic.