The Motorsport UK Yearbook 2023, otherwise known as the Blue Book, has the following rules:

12.21.2. Drivers must use the track at all times and may not leave the track without a justifiable reason. For the avoidance of doubt:
(a) The white lines defining the track edges are considered to be part of the track.
(b) A driver will be judged to have left the track if any wheel of the car goes completely beyond either the outer edge of any kerb or the white line where there is no kerb.

12.22. Breaches of 12.21.2 may be reported and/or determined only by:
(a) A duly appointed Judge of Fact and/or
(b) Senior officials through the use of suitable equipment under the control of the organisers.

12.22.1. Breaches of 12.21.2 may be penalised using the following:
(a) In qualifying if the lap on which the breach occurred is faster than any previous lap then that lap time should be disqualified. Note should be made on the result sheet of any times disqualified.
(b) During races the following scale of penalties should be applied:
1st breach – no penalty
2nd breach – warning flag
3rd breach – 5 second penalty added to race time
4th breach – 10 second penalty added to race time
5th breach – drive through penalty (12.26.(h))
6th breach – black flag

Care should be taken to ensure that all signals (flag and board) must have been displayed to the driver concerned before moving up the penalty scale. All penalties applied should be noted upon the result sheet.

Page updated by Peter Tattersall, May 2023