I know which scene you're talking about. I had always assumed it was Michael Palin or John Cleese playing the role, but it's hard to tell considering you only see the side of his face. IMDb credits a man named Andrew MacLachlan for playing the role, and MacLachlan's name does indeed appear in the credits. However, Warner had previously worked with Terry Gilliam on the film "Time Bandits," so he definitely had some sort of connection to Monty Python.