I think that every British actor appeared in the movies! I saw an interview with Bill Nighy who said that when he was asked to play Rufus Scrimgeor he was relieved as he felt he was the only actor left in Britain who wasn't in a Harry Potter movie.
Bill Nighy is an awesome actor. He has been in major franchises (harry potter, pirates of the caribbean), nerd favorites (shaun of the dead, hitchhiker's guide to the galaxy) as well as award winning and independent films. Comedy, drama, this guy is fantastic. Most recent movie of his that I have seen, Wild Target. Excellent movie.
Google Image Result for http://2.bp.blogspot.com/_g9FcMPVi7bk/TPZHc14Cb2I/AAAAAAAABNc/dVJh8VMka7g/s1600/Rupert-Grint-as-Ron-Weasley-Bill-Nighy-as-Rufus-Scrimgeour-Daniel-Radcliffe-and-Emma-Watson-as-Hermione-Granger-in-Harry-Potter-and-the-Deathly-Hallows-Part-I.jpg