I imagine doing GMC during full-on mixed mode must be a nightmare. Perhaps Gonzo could back this up?
I think we had a little taste of this post-BAW38.
Can't see it working, myself.
Heathrow Airport, EGLL is scheduled at 99% capacity. I'm not sure what Gatwick is scheduled to, but it's not that high. Believe me, that last 5% is where it gets difficult if anything out of the ordinary happens. It's going back a few years now, but after 11th September 2001 there was a global dip in commercial aviation. EGLL was running at about 10% fewer movements (1150-1200 rather than 1400 per day), and it worked like clockwork and seemed very, very quiet. When any ATC unit (tower, sector etc.....or controller, for that matter) is running at near-capacity, those last few percentage points actually increase workload exponentially.