Primary position

I think part of the problem is the language used in Bikeability. 'Primary' implies 'default' when, as I think general judgement on here is, it's actually an appropriate option in some situations. I would never use the phrase 'primary' with a client.

The primary position is the default position, but that's not the same as saying that you always or most often have to take it. It can be the default even if you use it less often than other positions. I wouldn't consider it an 'option', either. Which position you assume depends on how your risk assessment of an individual situation pans out. Your risk assessment should mostly give you a clear indication as to what is best to do. I don't think there are any situations in which a decision between the primary and secondary positions has to be taken and in which both are equally valid options (unless you were to count being all alone with no other road users around for miles, but even then in the secondary position you'd probably run a greater risk of coming off the carriageway, or it was your mother driving behind you who you know would be fully aware of you and keen not to harm you, etc.).