The biggest note in the UK is the £50 note. In my entire life I have handled one three times. Each time not a single business would accept them and I had to go to a bank to deposit it instead. Looks like it's a voluntary ban to me.
I admit it's difficult to spend £50 note, but it's not that bad. Supermarkets and restaurants accepts them all the time, as long as you are not using it to settle a £5 bill.
How can you trust the pounds nowadays with 1 in 3,333 being fake?
It's not often you run into a fake. I withdraw money from cash machines and usually change are in coins. Shops can be hit pretty bad with fakes though.