You're probably thinking "who", but I saw Ray Ashcroft on a train from Norwich to Sheffield way back in 1993. He later went on to play a detective in The Bill for a few years, but has appeared in all the big soaps. I also met, and had my photo taken with Portillo at Doncaster station a few years back.
Non-rail related, I was very good school friends with Ursula Holden-Gill who played "Alice Dingle" in Emmerdale. I lived on the same road as Myleene Klass in Gorleston, near Great Yarmouth, and even had a kiss with her at a college party, not that I attended the college but some friends did. Also whilst living in that area, I worked at a holiday park and half the camera crew for "Keeping Up Appearances" stayed with us. I got to watch them filming at Great Yarmouth Pleasure Beach and met all the cast. They were lovely. It was the episode where Hyacinth was on the 'merry-go-round', for any avid fans.
Sally Lindsey who played Shelly in Corrie bought me and my mate a drink in a bar in Manchester, all because I went over and asked, "Are you Shelly from Corrie". She was lovely!
Whilst working for a well known mobile phone company in Manchester I sold phones to Chris Bisson (Corrie, and now Emmerdale). He was a great guy, very chatty. I also sold a phone to Olly Gunner Solskaer (probably spelt that totally wrong) who played for Man United at the time.
When I was a kid I met Penelope Keith a few times. She was friends with a historian guy who lived on our small road in Colne, and she bought a house in the nearby picturesque village of Wycoller.
I've seen lots more, including the Queen, Prince Charles, Princess Di, Princes William and Harry, Cliff Richard, Brian Adams, Louise (from what was Eternal), Johnny Vegas, Ricky Tomlinson, plenty of Corrie and Emmerdale stars, and even Michael Jackson. None of these were at concerts by the way.