If you live in London you see celebrities all the time. It’s not such a big deal. In the provinces it’s very different.
If you spot Griff Rhys Jones whilst you’re on holiday in France, back home they’ll be calling you [forename] Griff Rhys Jones [surname] and asking you to relay the story every Friday evening.
They might even rename the pub after you. “The John Griff Rhys Jones Smith Arms”.