To be fair, never having seen Harry Potter or the later series of Outnumbered I don't really know who the chap is, but I'm sure some of you may do.
http://www.bbc.co.uk/news/entertainment-arts-30615934
On TV, character actor Ryall appeared in many well-known shows including The Singing Detective, Holby City, Casualty, Midsomer Murders, Goodnight Sweetheart and the Andrew Davies version of House Of Cards.