He introduces the rest of his motley crew - most of them stalwarts of the famous Comedy Store in London - and then proceeds to work through a number of knockabout games and exercises which test the performers' razor sharp minds and spontaneity to the limit. This is an hour of pure silliness, and the audience lap it up.
Merton by no means is the star of the show because that is not how it works. This is an ensemble effort, and the team's easy repartee and ability to play off each other shine through brilliantly. Granted, certain sequences can drag a bit and some are far funnier than others, but these are clearly skilled pros, embracing audience suggestions no matter how bizarre, and toying cleverly with them until they run out of steam. On the afternoon I attended, there was a story about Shakespeare and his kettle, a playlet showing the last five survivors on Earth, an Indian expert explaining how to cook for elephants, and a West End musical number from the maternity unit, the latter displaying unbelievably slick timing and rhyming from Suki Webster and Mike McShane.
Of course, an audience is guaranteed an entirely different show at each viewing, so the format never really becomes tired. Merton's usual mix of quicksilver wit, daft absurdity, and affable charm is a joy to behold, and as they take their bow, the Chums beam out ecstatically at the rapturous applause rippling through the auditorium. They have obviously enjoyed every minute - and so have we.