The following is a summary of the rules you must adhere to; there will be a BTF (British Triathlon Federation) referee in attendance; she may apply penalties and/or disqualifications if these rules are broken. 

• SWIM in the direction indicated by the swim starter (clockwise or anti-clockwise)
• NUDITY is not allowed in the transition area (or anywhere else!).
• HELMET must be on and fastened before you pick up your bike to start the cycle leg.
• NO DRAFTING - do not ride close behind or by the side of another cyclist, except to overtake
• SAFETY & HIGHWAY CODE - be safe at all times and observe the highway code
• RACK your bike before you unfasten your helmet at the end of the cycle leg
• ABUSE - do not shout abuse at marshals, fellow competitors or members of the public
• RUN & CYCLE on the left and do not cross the road centre line
• OBEY event marshals at all times
• SUPPORTERS are welcome to cheer from the sidelines but are not allowed on the course at any time

ALSO

• Know the event layout for exits & entries and the cycle/run course
• Rules in detail - as published by the British Triathlon Federation