Ok, Americans (and youngsters)... before watching it, please treat it as a joke sketch like the 4th Doctor's appearances on Jim'll Fix It and Animal Magic, not an extra episode, and look up Ronnie Corbett and The Two Ronnies on wikipedia so you get the jokes which depend on knowing who the little guy is (and why he's the wrong half of the double act to play a... SPOILER).
PS: Edited addition: the bowler hatted intergalcatic ambassador is straight out of The Tomorrow People. ;-)