Whatever we may think of proposals for a 'sugar tax' (I think it a thoroughly bad idea) this observation from a 'top nutritionist' takes the biscuit for ignorance of economics:
“If you make things that are desirable more expensive, this has no impact on purchasing,” Dr Carrie Ruxton told FoodManufacture.co.uk. “Similarly, if you make things like fruit cheaper, that doesn’t incentivise people either.”
I'm guessing that the study of nutrition doesn't include any economics. There are, I'm told, exceptional circumstances where making something more expensive doesn't affect demand but generally speaking making stuff more expensive means less of it is bought. Dr Ruxton (who has a PhD studying the relationship between children’s eating habits, socio-economic status and growth) clearly thinks that the laws of supply and demand don't apply.