1. A method ( 200 ) for use in a wireless cellular communications system ( 100 ), in which system there is a number of cells ( 110 ), each of which can accommodate a number of user terminals, UEs ( 112 ), with the traffic to and from the UEs in a cell being routed via a base station ( 114 ) of that cell, and in which system there is also a function ( 116 ) for the control of said base stations, the method ( 200 ) comprising: letting ( 210 ) the control function ( 116 ) of the base station ( 114 ) of a first cell ( 110 ) maintain 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 ( 112 ) in the first cell is in communication with, the so called Active Set list, letting ( 220 ) said first UE in the first cell measure and report transmissions from base stations in Neighbour Cells to the control function ( 114 ) of the base station of the first cell, letting ( 230 ) said first UE measure transmissions from base stations of cells which are not Neighbour cells of the first cell, so called Detected Set measurements, and report said measurements to the controlling function of the base station of the first cell, the method ( 200 ) being characterized in that it additionally comprises: letting ( 240 ) the control function of the base station of the first cell maintain a third list of parameters for other cells within a certain distance of the first cell, letting ( 250 ) the control function of the base station of the first cell use 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, letting ( 260 ) the control function of the base station of the first cell use the identified cell or cells in the Detected Set report to update the first UE's Active Set.