The "primary position" is a phrase that crops up a lot in British cycling, "taking the primary", "adopting the primary position" &c.
Certainly taking the lane is critical action you need to do on today's roads, but why call it "primary"? That's asserting that its the main place to be, and elsewhere is "secondary".
Cycling in gutter with buses going past and less than 1m of fading red paint doing nothing to keep you alive -yes, that's secondary.
Cycling along with parked cars to your left while you look in every window to see if there's someone there about to open the door -yes, that's secondary.
But is going down the middle of a lane full of heavy traffic "primary"? No: it's the bravery position.
Do it and you get hated by everyone who thinks they are being held up. They sound their horns, they punishment pass you, they may even brake check you afterwards. You can pedal hard and get up to speed, to lessen this a bit, but that works if you are fit, aggressive and willing to reach your destination after a workout. And in somewhere hilly -like much of Bristol and some of S Gloucs, it doesn't matter how fit you are, you will still be crawling as far as the impatient wanker in the van behind you is concerned -that the van driving about 2 metres behind you while he swears about arrogant cyclists.
It's the bravery position as you need to willing to mix with the vehicles of death: the HGVs, the buses.
It's the bravery position as if you look at the demographics of British cyclists, its males 20+, with the numbers petering out as they get older and unable to accelerate enough to "claim the road".
It's the bravery position as it completely fails to work once you reach dual carriageways or three lane gyratories. Take a lane in a gyratory or a roundabout with a motorway junction, and taking the lane is only for the very, very brave. There's the cars behind you who don't expect you to be there, the cars turning off the road and wanting to get to motorway speed -you have to sprint to clear their exit path alive. Then there's the cars coming off the motorway, not used to seeing bicycles, and not prepared to wait for any they do actually see. You want to be brave: negotiate the A4174/M32 roundabout.
So let's stop pretending that the centre of the road is the place to be. It's only the place to be because the standard UK alternatives are so fucking awful. And because of that, because its the bravery position, cycling is for the brave only.
Some people are happy with that and claim its the place to be. Well: there's Downhill mountain biking as a sport too -but that doesn't mean that you expect families to go to school with body armour so they can safely negotiate 4 foot drop-offs. If you are happy with the bravery position -go for it. Just as if you are like negotiating extreme DH courses for entertainment -great. If you like that, and your commute includes an extreme DH course, you are a lucky person. But don't go round advocating DH skills so that everyone else can get to work or school uninjured.
Take the bravery position if you want to: but recognise that it will forever be for the bold and the brave only -and stop imagining that it's "the primary position" -the place for a transformation in mass cycling to take place.