Babies are mostly fine switching formula. Very few babies would be made ill or uncomfortable by switching either permanently or occasionally.
Enough with the dramatics, Boudicca.
Mothers may prefer to stick with one brand and that's fine.
The marketing of formula is contained at present, by law. The reason for this is not because it's thought loads of people would put their babies at risk without it.
However, there is a risk that families on the margins of being able to cope at all, financially, may be encouraged to buy formula at one price, and then find it is dearer the next week. For a small number of families, this would be a bad thing. They might be forced into giving the baby something unsuitable instead eg ordinary milk.
I stress this is obv not a widespread risk in the uk. Only a handful of very vulnerable babies would be at risk. But that is the thinking behind the legislation.
The answer is of course permanent low prices.