I think that it is very dangerous for any road user to veto the movements of a following road user and this is the cause of much unpleasantness.
Hmm.
Not as dangerous as the cretins who routinely decide the pinch points on Manchester Road are THE IDEAL place to overtake, or those who'll insist on the same manoeuvre on blind bends, hill crests &c.
I see what you're saying Monty, but my experience of commuting drivers is that they're opportunistic, extremely short term planners, mostly unable to read my speed correctly, or anticipate hazards - they also seem to routinely underestimate the amount of distance that they should give me when overtaking. (Although it's possible that they genuinely feel an elbow brushing overtake is a pleasant experience, to give them their due).
I've even been beeped at for waving one bloke back (he was about to overtake me into the path of an oncoming coach that he'd either not seen, or couldn't see- another blind corner special). Some people *need* to be "vetoed".
The better ones (and there are some) hang back whatever road position I'm in at these points of danger - the majority[1] won't, and primary is essential not just to forestall a nasty overtake, but to give some escape room if they insist on attempting the manoeuvre (they'll generally go wider, if I start out in primary).
[1] My personal feeling is that that majority is shrinking, albeit rather slowly. Whether that's because the people I encounter every day are more used to seeing me, and know they can pass safely as soon as we pass the danger points (i.e. I don't "hold them up" per se), or because drivers are becoming more cycle aware generally, I couldn't say.