The Town and Country Planning (General Permitted Development) (England) Order 2015

Class R – erection etc of gates, fences etc by the Crown for national security purposesE+W

Permitted developmentE+W

R.  The erection, construction, maintenance, improvement or alteration of a gate, fence, wall or other means of enclosure by or on behalf of the Crown on Crown land for national security purposes.

Development not permittedE+W

R.1  Development is not permitted by Class R if the height of any gate, fence, wall or other means of enclosure erected or constructed would exceed 4.5 metres above ground level.