"...it would be preferable if people bought healthy, well-produced potatoes from their retailer, rather than grow their own"
I can't see why they should be criticised in this case.
So you agree with the Potato Council that it would be preferable for you to lift 20kg from Tesco rather than your allotment? I would have expected you to have joined me in criticising such a statement.
This year potato farmers have been hit hard, with a reduction in production by about 5%, so I'm sure they would be happy to gain an extra 1% next year. Every little helps.