In my last school some of the the toilets had to be locked during lessons because there weren't enough staff to police all the blocks and someone was smearing faeces on the walls.
The school before that some of the toilets were locked because a group of boys ripped a toilet off the floor, so anyone allowed out of lesson had to go to the reception ones.
Schools desperately need more funding for adults on site to safeguard our young people. It's simply not safe for them to be out of lessons unsupervised now.
Not going to lessons is unlikely to get the school extra funding to make unlocked toilets viable.
I don't teach in schools anymore, I couldn't deal with having to decide who could go to the loo when and getting it in the neck either way.
Let them go and SLT are on your back. Especially if they get up to something. Don't let them go and it's against their human rights. Ask them to wait 10 minutes (to reduce the chance they're meeting their mates to film a tiktok) and they'll disrupt that ten minutes of the lesson moaning.
The girls in my year 8 tutor group telling me daily they did not have time to go at break because there just aren't enough toilets, at one point being scared to go in because they shared with year 10, and no hot water for months, passing it up the chain and nothing ever being done.
Skirt length, I don't care but I do think it's pretty disrespectful to themselves and others to be showing their underwear. They had the option of trousers in both schools I worked in, if a skirt that fitted and covered the areas that needed covering was an issue. Boys weren't allowed to have their underwear on display either. If they don't like the uniform I don't think protesting by not going to lessons is a productive method of changing that.