Stephen Hawking appears in the A-Z documentary on the Red Dwarf II DVD! He says why he likes the show:
"Unlike some science-fiction series, Red Dwarf does not take itself too seriously and does not try to be politically correct. This allows it to do stories in situations that Star Trek would never dare touch."
He later said that 'Back to Reality' was his favourite episode. Sir Patrick (Moore, Stewart, who's not a Sir, also puts in a few words) also makes an appearance looking healthier thand he should. Can't wait for the movie. =D