Interpreting Permissions and Consent
The basic rule is that if the permission or consent is on the face of it a complete and self-contained document there is no immediate need to look beyond it in order to interpret its extent and terms.
If it incorporates other documents by reference, perhaps by a list of drawings, then those documents should be taken into account, but no others. There may, of course, have been many other documents that were submitted as part of the application or later as a means of persuading the decision-maker to give permission, but these do not form part of the permission and should only be referred to if needed to resolve an ambiguity on the face of the permission.
It is therefore essential to ensure that every aspect of the works that makes them permissible is captured by the words and documents referred to in the formal notice of permission or consent issued by the local planning authority.
For example, if what makes an application acceptable is the detailed design and materials that define its aesthetic impact, these aspects will need to be clearly part of the permission or consent, or the outcome may not be as envisaged at the time permission was given.
Also of interest...
Planning Permission in relation to listed buildings, conservation areas and other historic places.
Listed Building Consent
Scheduled monument consent is required for most works and other activities that physically affect a scheduled monument
Works in a Conservation Area
Neighbourhood Development Orders
Development Consent and Heritage
Advertisement Consent and Heritage