Like Mao, the rules to Mornington Crescent are too simple to go into. If you are really interested, listen to the Everyman's Guide to Mornington Crescent, included as a bonus on the BBC cassette 'I'm Sorry I Haven't a Clue 2', and which goes into the history and rules of this cultural phenomenon, going back to Roman times and the origins of the game.

As to popular rules, the major experts of the game, as seen on I'm Sorry I Haven't a Clue, usually disallow straddling and shunting, but sometimes allow passing of water during play, and often play the famous Ongar move on the diagonal.