Highway Code Rule 5

Organised walks or parades involving large groups of people walking along a road should use a pavement if available; if one is not, they should keep to the left. Look-outs should be positioned at the front and back of the group, and they should wear fluorescent clothes in daylight and reflective clothes in the dark. At night, the look-out in front should show a white light and the one at the back a red light. People on the outside of large groups should also carry lights and wear reflective clothing.