Neweternal radical uniform change is what a super head does when brought in for a 3-5 year blitz to "turn around" a failing school.
It's not done because uniform itself has any impact, but because its a very easy way for the new head to signal regime change.
It's done for the same reason dogs pre on lampposts.
Those heads are given thumping great budgets the likes of which the school hasn't seen before and won't again, to bring a school up from special measures to good. They redecorate, buy in new equipment, change school hours (often cutting out as much break time as possible to keep the kids on a very short leash. They have special hiring and firing freedom and usually change 3/4 if the staff.
They do achieve improvement, but it's not because of the uniform, but because of special measures emergency freedom to hire and fire and a big budget.
The new uniform and Draconian enforcement is only chest thumping to say "the silverback has taken over and this is not a democracy".
If there were already a shirt, tie blazer uniform they'd change the colours or make some other posturing change to scent mark the school and children.
I've been one of the teachers brought in by a superhead in Merton. The uniform was the most visible change to the public but the least fundamental to the turn around inside the school. It certainly has no lasting impact on results, that's down to the new staff actually staying and the massive cash injection schools get in those circumstances being used wisely.