Is it not against the law to overtake on the chevrons, the BMW driver is showing little consideration but plenty of impatience, and should have merged behind the Discovery instead of trying to jump him over the chevrons, it's not like the BMW driver was for gaining much advantage.
How many times have you been slowly filtering in such a situation, giving way and being courteous to other road users, then you get a right prick who shows disregard for others by speeding up the outside lane over the white lines and dives into a gap that was never there, then flicks the finger at you if you don't let them in quick enough.