Perhaps the continuing decline in the currency's value will give us an opportunity to see £50 notes more frequently. I don't think I've seen one more than twice in the past 12 years, and I get cash out less and less frequently.
Getting currency exchanged before a trip? They give huge bills.
Buying a used phone or furniture from Craigslist? Are you going to pay with 100 twenties?
New ATMs even ask you the breakdown of bill sizes you are want.