I've never handled a £50 note. (I am young enough that if you gave me £1 for every year I've never handled one, I wouldn't be able to afford one. But I am old enough that I could dip into my lifetime of savings to make up the difference.)

A friend's dad showed me one when I was at school - that's it. He seemed amused I hadn't seen one before, then after making a minor show of it, as if it was some precious, rare item, said he'd never previously seen one either. They've been uncommon my whole life, and apparently could/can be difficult to actually use, shop assistants being unfamiliar with them and not confident in their legitimacy.

I expect today most people would use bank transfers for the sort of sum where the sheer number of notes would make a £50 one useful.