It was sitting around in a dark, damp, tent in Wales one evening, when we arrived at the following rules for 21. They are set down here for posterity, along with the generic rules for those unfamiliar with the method of play.

The structure of the game is simple;

• The order of play is established. This is most easily accomplished by sitting in a closed outline shape (such as a circle) and playing around this shape. However any established order of play will work but other orderings can create considerable extra difficulty.
• Players take turns to count aloud to twenty-one subject to the given rules.
• The first player will establish the direction of play. Play starts in this order with each subsequent player continuing to count
• If a player counts two steps the direction of play is immediately reversed
• If a player counts three steps play skips one player in the order, in the given direction.
• The counting is subject to the current rules listed below
• If a player fails to adhere to these rules then he must drink. Counting then starts again at one with that player
• The player to say twenty one must drink but is then permitted to add or remove a rule

The current rules are;

1. All odd numbers are to be in French
2. All even numbers are to be in roman numerals
3. All numbers containing a two are to be replaced by the phrase 'in the tent'
4. All multiples of five are to replaced by the phrase 'on a dark and stormy night'
5. All multiples of seven are to be replaced by the phrase 'by a hairy canoeist'
6. All prime numbers are to be replaced by the phrase 'with' and then your own middle name
7. All multiples of four are to be replaced by the phrase 'with a lemon'

The order of priorities is;

• All other rules take priority over 1 and 2
• 3, 4, 5, 6, take priority over 7
• 3, 4 , 5 take priority over 6
• 4 and 5 take priority over 3.

The following ground rules also apply. They must be strictly adhered to for the entire duration, breaking one of these rules must be followed by immediate drinking.

1. All drinking with the left hand, pinkie extended
2. No swearing
3. No pointing
4. No first names
5. No mentioning of the word "drink" in any form, including verb, noun, gerund, adjective, adverb etc.