In my experience, in the UK, the rental agency required 12 months rent in advance (plus another 2 months rent as deposit) when I was self-employed. They would have accepted monthly rent if I had 5x the annual rent in cash savings, but I didn't.

And then every year after that they required another 12 months rent up front, when it came to the annual tenancy renewal. Track record of paying the rent wasn't good enough to prove that I could keep paying the rent.