Suppose Alice has a restaurant where she serves pies for £10. She can make them with gluten free bases for the allergic, and these bases cost her £3 over the regular ones' £0.5. However, to make one a gluten free pie, she charges £14 thereby profiting more from the allergic than the non-allergic. Is she committing unlawful discrimination or otherwise behaving in an unlawful manner?
Edit: I think the rationale is most likely they see that many people are willing to pay more for the gluten free so they charge extra. They don't realize that for some it isn't a choice and so thus their attempt to profiteer from a trend could possibly be illegal.