Without prejudice to the provisions of this Part as to the duration, revocation or modification of planning permission or permission in principle, any grant of planning permission or permission in principle to develop land shall (except in so far as the permission otherwise provides) enure for the benefit of the land and of all persons for the time being interested in it.
Where planning permission is granted for the erection of a building, the grant of permission may specify the purposes for which the building may be used.
If no purpose is so specified, the permission shall be construed as including permission to use the building for the purpose for which it is designed.