I'm not shooting anyone @MsAsparagus , but as @Shinyandnew1 has explained here, and several other posters afterwards, the Gvmnt funding has been something politicians have thrown out promises about, to win a few votes, for a few years, without actually doing any research about how a Nursery runs, and what is involved.
I don't see how anyone can think so many children can be subsidised by fewer and fewer paying children, for every hour.
This Nursery is having to charge £8ph for the hours you pay for, to make up for the fact they make a loss on the hours the Government are supposed to fund, but, in fact only part fund.
FWIIW OP, I think £8 if it is for one meal, would be huge. If it is for all the meals and snacks across the day, then less so, but either way, if there is an option for you to send in food and not pay it, and that is what you have chosen, then they should not be retrospectively billing you for something you have opted out of.