1. A method for use in a wireless cellular communications system, in which system there is a number of cells, each of which can accommodate a number of user terminals, UEs, with traffic to and from the UEs in a cell being routed via a base station of that cell, and in which system there is also a function for the control of said base stations, the method comprising: maintaining, by the control function of the base station of a first cell, a first list of cells which are in the vicinity of the first cell, a Neighbour Cell list, and a second list of cells which a first UE in the first cell is in communication with, the Active Set list, measuring and reporting, by said first UE in the first cell, transmissions from base stations in Neighbour Cells to the control function of the base station of the first cell, measuring, by said first UE, transmissions from base stations of cells which are not Neighbour cells of the first cell, Detected Set measurements, and reporting said Detected Set measurements to the control function of the base station of the first cell, maintaining, by the control function of the base station of the first cell, a third list of parameters for other cells within a certain distance of the first cell, wherein the parameters of the cells in the third list include the position of the cells, and the antenna direction or directions of the cells, using, by the control function of the base station of the first cell, the identified cell or cells in the Detected Set report to update the first UE's Active Set, using, by the control function of the base station of the first cell, received Detected Set measurement reports from the first UE and said third list in order to determine the identity of the reported cell or cells of a Detected Set by using the position and antenna direction of candidate cells in the third list to perform a path loss calculation to determine the identity of a Detected Set Cell.