Right, I can see the weight of consensus is that the vehicle going straight on (A) has priority.
So here's what actually happened...
I was turning right as vehicle B.
I *think* I crossed my line marginally before the taxi that was vehicle A, secure in my belief that I had right of way as I was crossing his give way on the main road (ok, I was wrong it seems) but prepared to stop as it's one of those ambiguous junctions where most of the time people tend to just sit there, play it safe and wait for someone else to make a decision.
Not this time.
The taxi pulls out on me but we both stop (I was expecting it). I assume he has decided to let me go, nod and smile my thanks and proceed on my way, passing in front of him.
At this point (I'm directly in front of him now) he blasts his horn at me, nudges forwards towards me, revving his engine and gives me a torrent of shouted abuse. I carry on as I'm committed by now anyway and respond to his abuse that perhaps he should explore the possibilities of sex and travel (I tell him to f... off).
Carrying on down the road. a glance over my shoulder shows that he is turning about in the road using forward and reverse gears in order to pursue me. Great, here we go. There is no other traffic (i.e. witnesses) in sight.
So he screams past me inches away, horn again blasting and shouting abuse and then jumps on his brakes in front of me, carrying on the length of the road at about 10mph in an attempt (I presume) to annoy me by slowing me down. Shaking my head, I carry on without rising to it, holding back far enough to react if he is to do anything else unexpected until at the T-junction end of the road he gives me the Vs and screeches off in a cloud of self righteous tyre smoke.
It seems my passing in front of him and delaying him by 2 seconds is worth adding another several minutes onto his journey and risking losing his career thanks to a dangerous driving charge just to prove he was right. It's one of the few times I wish I had a helmet camera.
Guess I'll know next time... thanks for all the input!