Living and working in London, in the mid 60s, 70s and early 80s I often came across actors. pop stars and the likes in bars, cafes and department stores, etc, but the one I saw most often was Peter Vaughan, mostly in the original, family-run Patisserie Valerie in Soho, where everyone was expected to share a table and the cakes were left on a stand on each table so you could help yourself and admit to what you'd eaten when you asked for your bill (amazingly, it seemed to work). Even after I'd left London I did come across him once again, and it was a rather bizarre coincidence: on a family visit to Croydon about 15 years ago I bought a DVD of the film 'Straw Dogs' which was banned for decades after its making in the early 1960s - Vaughan had a substantial part in it, I then boarded a tram to East Croydon Station and went to catch a fast Victoria train. When the train pulled into the platform I went to open the nearest (slam) door and there ensconced on a 3-seater with suitcases around him and all over the opposite seat was Peter Vaughan (at a guess, having got on at Gatwick). The glare on his face indicated he had no intention of sharing his surrounds so I quickly moved to the next compartment, and thought better of asking him to sign my DVD! (Not sure how you'd do that anyway)
P.S. I read today that he only ever appeared in 3 episodes of 'Porridge', but for 30 years afterwards he'd endure 'so they let you out, Grouty' in the street.