The OP was talking about pairs of cyclists, not groups, so let's deal with that rather than get involved in group etiquette.
Yesterday coming back from a big cycle event we were held up endlessly by queues of cars held up behind pairs of cyclists riding 2-abreast on very busy, but narrow, A roads.
On the event itself we were also held up several times by slower riders ahead going 2-abreast and causing a tailback of cars, which we couldn't safely overtake.
What the hell is wrong with singling out if you become aware that you are seriously holding up traffic? Not doing so is purely selfish IMO - nothing to do with safety or "legality" - these are smokescreens that the righteous arrogant cyclist hides behind.
Yesterday coming back from a big cycle event we were held up endlessly by queues of cars held up behind pairs of cyclists riding 2-abreast on very busy, but narrow, A roads.
On the event itself we were also held up several times by slower riders ahead going 2-abreast and causing a tailback of cars, which we couldn't safely overtake.
What the hell is wrong with singling out if you become aware that you are seriously holding up traffic? Not doing so is purely selfish IMO - nothing to do with safety or "legality" - these are smokescreens that the righteous arrogant cyclist hides behind.