From the Outdoor Access Code:
RESPONSIBLE BEHAVIOUR BY THE PUBLIC
Access rights extend to cycling. Cycling on hard surfaces, such as wide paths and tracks, causes few problems. On narrow routes, cycling may cause problems for other people, such as walkers and horse riders. If this occurs, dismount and walk until the path becomes suitable again. Do not endanger walkers and horse riders: give other users advance warning of your presence and give way to them on a narrow path. Take care not to alarm farm animals, horses and wildlife. If you are cycling off-path, particularly in winter, avoid:
• going onto wet, boggy or soft ground; and
• churning up the surface.
RESPONSIBLE BEHAVIOUR BY LAND MANAGERS
Where possible, work with your local authority and other bodies to help identify paths or routes across your land which are suited for cycling. If you need to put a fence across a path or track then install a gate which allows multi-use access.
And
Outdoors. This term includes mountains, moorland, farmland (enclosed and unenclosed), forests, woods, rivers, lochs and reservoirs, beaches and the coastline, and open spaces in towns and cities.