Yes, they do have to pay 25%.
They're being given two lump sums. One is for general Covid costs (extra cleaning, supply teachers, photocopying, etc). My understanding is this isn't based on need. It's a basic lump sum.
I think the second amount might be based on need (need to check), but schools are expected to make up the shortfall from their general budget. Schools with more needy pupils will have to dip into their Covid budget, which they're already spending on Covid! 
Meanwhile, many schools are still waiting for their promised laptops.