Back in the 2000s/10s I had a little jar of various £1 and a couple 50p I was certain were fake. Interestingly the fake £1 I got most frequently were -from- vending machines - I wonder if those refilling them slipped them in?
Sadly not sure where they are now, they were also mixed in with a good few £5 coins I bought, I used to love paying for things with a £5 coin. Hope I find them again!