I don't rely businesses who require cash for big purchase. Big purchase need to be proper documented and small purchase is okay with cash to meet daily basic needs.
No, I never faced any difficulties for using cash as seems everyone welcoming cash.
Government can ensure that options for using cash and card are always stay side by side.
London is a multicultural city and have peoples from different abilities and not everyone have a bank account in UK to use them to buy stuffs. So they needed to access for cash.