Section 73 (s73) of the Town and Country Planning Act 1990 allows for planning applications to be made for the variation or removal of a condition on an existing planning permission. Different forms from those used for ordinary planning applications are required for s73 applications. When determining such an application the local planning authority can grant the application, i.e. remove or vary the condition as requested, refuse the application or impose different conditions to those imposed on the original grant of permission.
National Planning Practice Guidance contains further information on discharging and modifying planning permissions once permission has been granted.