That just depends where you live and work.

In a part of London with many tourists, I saw them used by people ahead of me in the queue daily. There are some cash machines somewhere in London that dispense them -- possibly in Canary Wharf, I forget.

Conversely, I don't think I've seen a cash machine with fivers.

https://imgur.com/a/sJu9y (cash machine showing it has £20s and £50s).