You don't want to be told your anger is misplaced, OP, but it truly is.
I am a teacher and also a school Governor and the budgets look AWFUL. One teacher was off long-term sick and it has totally destroyed the budget (which is absolutely not her fault, obviously! It's a horrible situation). We are cutting and scrimping everywhere to make ends meet. At the beginning of the financial year, we have to set a budget and we are not allowed to set a budget that is in deficit, but there isn't enough money - so absolutely everything is squeezed. We have no pencils in my classroom at the moment. I've bought class sets of pencils, glue sticks and felt tips for my class just so they have basics for learning. I'm far from the only one.
The Head is like the electricity police. She goes round turning off lights so that we are teaching half in the dark. She goes round turfing teachers out of their rooms and into the staffroom at lunchtime - not because she worries about their workload or stress - but because she wants to turn off the computers and the lights in all of the classrooms. It has got that silly.
What is happening is a national disgrace - and this is actually quite a smart solution. Staffing is, rightly, the largest cost in a school - and the one thing it is not wise to scrimp on. Not paying cover teachers to cover PPA is one of the biggest savers in terms of costs. It also means that teachers will be able to plan together and hold meetings and do things that would benefit your child's learning in a way that 2.5 hours of PPA, on their own - often with no quiet place to go - doesn't provide.
Saving in this way also means that experienced and highly qualified teachers might not get squeezed out for being too expensive. We are experiencing a brain-drain in schools because newly qualified teachers are cheaper. Why employ an experienced, highly skilled teacher for twice the cost when you can take a newly minted teacher for half the cost?
I totally get that it's inconvenient and annoying. I would be equally screwed in this situation as a single parent/teacher who would be working on a Friday afternoon - but please don't blame the school. They won't want to be doing this either. There is just no money. And that is entirely down to the Government trying to wash their hands of schools by underfunding them into oblivion until they have no choice but to become academies.
Write to your MP. It is an unacceptable state of affairs.
And it's not down to the school. Trust me on that.