From what I know there isn't a grant anymore. But I think schools do get a small amount of funding for school clothes. They have to do this as it could mean a child doesn't get the education due to uniform. Schools tend to keep this quite do to the lack of funding.
There are several ways to try to get help with school uniform. School essentials grant, and clothing allowance scheme. Sure you apply via .gov. That said, I don’t think they are that easy to get and not everyone knows about them.