Whip Rule as per the BRC hand book

G23.1.1: Whips The use of the whip must be for an appropriate reason, at an appropriate time, on the correct area of the horse and with the appropriate level of response.

Appropriate Reason: The whip must only be used as an aid to support the natural aids in encouraging the pony/horse forward, or to help the rider to encourage the pony/horse in the right direction. For example, it may be used down the shoulder to keep a horse straight on the approach to a fence.

It must never be used to vent a rider's temper; any use for such a reason is automatically excessive. 

Appropriate Time: As an aid, the appropriate time is when the pony/horse is reluctant to go forward under natural aids i.e. seat and legs. Its use, for instance, after a refusal is excessive.

Its use after elimination is excessive.

Right area of the horse: As an aid to go forward the whip may be used down the shoulder or behind the rider's leg.

The use of a whip on a pony's/ horse's head or neck is always excessive use.

Appropriate Level of Response: the whip should never be used more than three times during any incident; and if the pony/horse is marked by the whip (skin broken or a welt) its use is excessive.

(The rider is expected to know if the pony/horse has sensitive skin and must use the whip accordingly). The arm should never be raised above the shoulder whilst using the whip. The whip should always be carried and used in the backhand (handle pointed upwards) position and never in the forehand position (handle pointed downwards). Misuse of a whip: If, in the opinion of the judge/official, a whip is misused/ overused the rider may face up to 25 penalties or disqualification at the discretion of the Official Steward