Cyclists two abreast are easier to deal with than two in line. Let's say a cycle is 2ft wide, the cyclist is likely to wobble and swerve to avoid potholes and other road irregularities, (but these can be observed by the following driver), so the cycle needs 3ft for his wobble/swerve. Then we need a little extra margin for safety, so add another foot. That's 6 feet from the kerb. So as we overtake, our left mirror should be 6ft from the kerb, so we are using most of the opposite carriageway. Why not use it all as if we were overtaking a car?
A bicycle on its own, near the kerb will encourage cars to pass between the cycle and the oncoming traffic. Two abreast effectively become a car, so we have to overtake properly. Two in line are much more difficult to overtake as so much more distance is needed and we are starting from a low speed.
Four cycles in a line are almost impossible to overtake safely, but two pairs are like overtaking a large van. Much easier and quicker.
My pet hate with cyclists is a varying speed. If their speed is constant, I can plan and deal with it. If traffic prohibits me from overtaking, a constant speed is manageable. When their speed increases and decreases, this is so much more difficult to handle. The lycra brigade seem much more likely to vary their speed. A middle-aged lady in a village on her way to the post office, pedalling slowly but consistently is so much easier to follow and to overtake when space permits.
Fun can be had on roads with solid white lines. We can cross the white line to overtake a cyclist, only if they are doing 10mph or less. (Highway code rule: 129) A nice uphill slope is ideal. Cyclist pedalling his socks off, aware of the car behind just following gently, but doing 11-13 mph, working hard and very uncomfortable. If he just slows down below 10mph, I can overtake. If the view permits. Makes me smile every time.
Strangely, we are not permitted to cross the white line to pass pedestrians, unless they are a stationary obstruction. (Email exchange with Dept. of Transport a few years ago, apparently this was not thought of in the original legislation as it was expected that pedestrians would take to the verge.) To deal with joggers coming towards you, pull in tight to the verge and stop. Let them deal with you as a parked car. (Other traffic and circumstances permitting.)