ATM’s in Britain do not withdraw that denomination (they max out at £20), unless for some reason an individual wants a £50 note: they would have to visit a bank requesting for that (banks stockpile bills of all denominations). However, there is a stigma with a £50 note (money laundering, drugs, etc.) as often depicted in news stories about criminals caught with “dirty money” often have £50.
Even if you were to spend it at a store: they are like “sorry, I have to get my manager” to verify it’s authenticity, due to concerns of counterfeit despite the new bank note series being printed from polymer. I’ve heard that is often reserved for business related or larger transactions at certain stores (electronics, luxury brands) where they may be inclined to accept £50 in multiple quantities.
Oh, it’s a country specific thing then. In the past few decades, I’ve used electronic money more than physical money. Applies to salaries, cars, shopping etc. Works with small merchants too.