Had a weekend in London and spotted several courier bikes – assuming fixed wheel (?)- some had some really fancy looking kit on them but one in particular had bars that must have been barely over a foot wide… Got me thinking, would it be like trying to ride a mini scooter and horrible or super sensitive to allow diving in and out of cars etc?

You’d get used to it.

All road bikes have narrow bars and are horrendous to ride thus. But like he said, people seem to get used to it.

i think the idea was that it is supposed to help you squeeze through tight gaps. although now it’s just a fashion statement (most of those types of bar are narrower than your shoulders or feet width or hips so actually encourage riders to go through gaps they won’t fit through)