Chris, he was Professor Cavor in "First Men in the Moon." Terry Thomas isn't in that picture. That's the one based on the H.G. Wells story with the insect-like Selenites that live in tunnels under the lunar surface.
You may be thinking of "Rocket to the Moon" where he indeed was paired with Thomas as a comic baddie. They end up in Russia and think they are on the moon. Also stars Gert Fröbe.