I ride regularly. I am also a qualified ride leader.
This thread is depressing.
Riding in London, I ride past all the traffic. I certainly don't hold it up. Even if a bus is stuck behind me for 20 seconds, I catch up with the traffic at the next junction and leave the bus behind. Filtering is permissable, but I always overtake on the right rather than overtake.
Primary position - to keep cyclists safe, and motorists too! When correctly used, primary postion is telling you it is NOT safe to overtake. When it is safe to allow traffic behind me to pass, I will pull into secondary position. If it is single track, or weaving around parked cars, etc, I do slow or stop to allow traffic to pass where it is safe to do so.
I cycle with my twins, they are 9. They've been riding bikes since they were 2 and on the road since about 6 or 7. I cannot believe how many people try to cut them up, or drive straight at them around traffic calming measure, trying to force them into the gutter. They are extremely proficient and won't wobble. But many cyclists do need SPACE! There is a new campaign running, - SEE cyclist THINK horse!
Riding two abreast - if I am leading 8 cyclists, and they are all riding single file, you have the equivalent of a very long HGV to try to overtake. By keeping my group close together, you can overtake once it is clear.