I won't lie, I'm split on this one. If I'm in a city and the speed limit is 25 and they are going 15, I'm patient behind them. The next traffic light is going to slow me down more than a pair of bikes. If I'm somewhere rural, the speed limit is over 50, and im on a road that sees about 10 cars an hour, yes you have the right of way, but it feels really inconsiderate not to move over for a couple seconds to let someone pass.
a) that road definitely is not with a speed limit over 50 and b) you cannot pass even a single bike here in a safe manner, in Germany for example it would be a misdemeanor to even try.
The speed limit on that road is 70km/h. I commuted to work on it last summer. I suppose it looks a bit slimmer than it actually is. It's perfectly possible (and legal) to pass a bike safely, or even meet cars. The latter is a tight fit and you'd of course reduce your speed appropriately.
Well in those cases the UK highway code rule 66 says "Be aware of drivers behind you, and allow them to overtake (e.g. by moving into single file or stopping) when you feel it is safe to let them do so."