Replenishing salt loss on day rides if you have hypertension

[mattr]

But the GP insisted that I really shouldn't eat those crisps.

Maybe time to find a GP who has some handle on exercising/sport?

I've been unable to find anything about this on the web,

Did some more digging and found a couple of studies (or at least the summaries) showing that the more exercise you do, the less impact salt has on blood pressure. So if you are really pressing on with training and suchlike, it may be worth trying some hydration tablets, but at a lower rate than recommended?