I know we've discussed Hue And Cry before and I love it. I meant to reply to your post in Curtain Call actually. I really enjoyed his performance in that, as I liked how fragile his character was. Writing adventure stories, but far too timid to take part himself!
He was excellent in Hitchcock's Stage Fright, a relatively unusual film for him to be in. In a lot of Hitchcock's films you can sometimes find a character or two that represent the director and I think Sim was that in Stage Fright, a cheeky old man who can't resist being an amateur detective!