I don't think that, legally, infant and junior schools can insist on a uniform. They can suggest a colour scheme, e.g. grey trousers/skirt with yellow polo shirt and grey sweatshirt. This wouldn't necessarily be a problem for most people's pockets if they can source it in local shops. However, I'm not sure they can insist that you buy from their suppliers, or that the school's logo is imperative.
If your school does insist on this and indicates that they intend to discipline any child who doesn't comply, then you could take the matter to the board of governors or even the local press.
Are they going through a consultation process with parents? Would seem sensible.
At the boys' school, they have a uniform, including a logo, but parents can choose to send their child in a plain polo shirt or sweatshirt provided it is in the appropriate colour.