Flexible working paycut - same workload

[Gf0rce]

My employer has reluctantly agreed to 4 day week.
They have advised I will need to take a 20% paycut and when I asked what work 20% of my job would be taken away (so I am clear and can have the 4 day week trial period made permanent) I was told they expected me to do 100% of the job I was doing before for 80% of the money and that if I didn't think it were possible I would have to go back 5days.

Are they allowed to do this? It seems unreasonable. I can find very little online about the legality around this, can anyone help?

Have you put in a flexible working request? Did you state a case for how the workload could be reorganised?

Jeez. Ring ACAS in the morning. I'm assuming you don't have a union if you're asking here, but this might be the moment to find out if you have any legal services included with your contents insurance or bank account, if any.

I went through the appeal procedure (after flexible working request) to get agreement to 4 day trial period.
I don't have a union, so any advice on this would be much appreciated
Thanks

I didn't lose any work load when I cut down from full time days to part time (school hours) I just work harder with a focus on managing my time and am very grateful they let me change my hours.