In reply to JamButty: There's a difference between
choosing to give way because it errs on the side of caution (or even politeness) even though it's actually your right of way, and being
forced to give way because you'd be dead if you didn't.
I realise that Chris hasn't clarified the exact sequence of events in his example.
(I don't think the driver of the M-series BMW who pulled out on me at the roundabout near work yesterday morning was worried whether I chose to give way or was forced to, so long as I ended up behind him.)