I'd pull out in good time to get through the pinch point without signalling right. Then signal left.
IME, pulling out without a right arm out risks a very very close overtake or even getting knocked off.
what would happen if everyone did it? It would either be bloody confusing all round or would become so understood as to negate its effect
A bit of confusion might not be a bad thing, everyone will have to slow down a bit. I still have have my right arm out and that prevents a close overtake.
And what about traffic on your left? Pedestrians about to cross the road you want to enter and scooters or other cyclists who will naturally overtake you on the left in the belief you're turning right.
Obviously I take notice of who's around me. If someone's about to cross the side road, I slow down give way. I rarely see other cyclists in SE London, apart from on the major through routes at commuting times. And there's usually no space on my left anyway.
The roads I tend to do this on are not the main roads but the residential through routes. The former has heavy ans slower traffic and close overtakes are less of a problem, unless there are clear stretches of no traffic. The latter are rat runs and drivers drive like dickheads and make cycling very unpleasant.
Indeed (when cycling) I tend not to signal left turns at all, unless there's someone waiting to pull out from, or pedestrians looking like crossing, the side road.
That's a very good point. I usually don't signal when approaching a T junction.