Primary position

BMMF, I bet you ride in the primary position on dual carriageway streets in London a lot. There is very little point in taking the primary position on a major A-road out of town, and certainly not for long distances. There will, however, always be situations even on roads like that when it is advisable to take the primary position for a while, e.g. at junctions.

Depends. Riding round multi-lane gyratories in London like vauxhall cross, elephant and castle I would rather be in the middle of a lane which is less confusing for everyone, drivers have to slow down to accommodate me.

I'm pretty sure that BMMF wasn't referring to that sort of scenario.

Even riding on the A406 when it is fast moving I ride in a manner that drivers still have to focus when passing me. I look at them as they pass and if one looks too close I have an escape route to my left

Yes, but you wouldn't fully take the lane, would you? On most A-roads, I ride further out than most people would, but not in the primary position. For instance, on the A104 Epping New Road, I have to ride further out than I feel comfortable, because someone put an absolutely stupid and counter-productive cycle lane with cat eyes right where I would normally ride.

Bus lanes form dual carriageways.

Er? Did you mean 'multi-lane environments' instead of 'dual carriageway'? A dual carriageway is of course one with some kind of dividing feature between lanes in opposite directions.