Random fact: £50 notes are the only note that is cheaper to make than it’s face value.
IE it’s very common to forge them as the gains are huge. Shops steer away from them if they can, far too many good quality forgeries around. Plenty of forged £20 and £10’s about but they tend to be lower quality and easy to spot.
The fivers in ATM’s has been growing for a while now, since the credit crunch basically. People find it easier to budget their weekly spend if they have X amount of cash in their wallet, this grew in popularity around 2009 so more fivers were required. The BofE directly told ATM operators to stock £5 notes as a quick way to get a load into circulation, Natwest/RBS and Tesco were the ones to do it first, mainly at sites where they had 2 machines. One would be £20 and £10’s the other would do £10’s and £5’s. Proved very popular.
Current predictions are that cash use will drop by 50% in the next 10 years thanks to contactless/digital payment methods so the days of a large wedge of cash not generating some suspicion at shops/banks are numbered.