Statutory guidance: Cost of school uniforms (Updated 23 October 2025) looks useful. Here’s some stuff that stands out to me:

Assess the overall cost implications
Schools should assess the overall cost implications of their school uniform policy…: for instance, when a child may grow out of an item quickly or where spare items are likely to be needed.

Avoid frequent changes
Schools should… show how any change in uniform specifications secures the best value for money…

Schools should take action to minimise any financial impact of any change on parents (such as allowing pupils to continue to wear the old uniform for a reasonable period or… only introducing new uniforms at entry or transition points in the school).

Consider how costs affect different groups of pupils
Schools should consider how the cost of their uniform might affect… families on very low incomes.

Engage with parents and pupils
Schools should… be able to show how these views have been considered in their policy.

Avoid needing additional uniform for extra-curricular activities
Schools should avoid requiring parents to purchase additional uniform for the purpose of… sport, music or drama.

I cut out a bunch because it’s wordy at times, the link above is worth a full read though. It also has some non-statutory guidance on linked pages. I don’t see anything to make an argument against the changes a slam-dunk knock them for six(? I’m on the wrong side of the pond to know how to use that) but I think there are some threads you can pull there.