A scheduled monument is one which is protected by the Ancient Monuments and Archaeological Areas Act.
Ancient Monuments and Archaeological Areas Act 1979 - Legislation website
The condition of scheduled monuments is monitored regularly by English Heritage.
Consent to work on a scheduled monument
You must have written permission before working on a scheduled monument.
Scheduled monument consent - English Heritage website
The Department for Culture, Media and Sport are responsible for Scheduled Monument policy.
Scheduled monuments - DCMS website