The disclosure provides an improved method of operating a mobile terminal or user equipment in a cellular telecommunications network to efficiently discover preferred cells, in particular a HeNB, prior to connecting. Whilst constant searching for a preferred cell can ensure it is found as soon as it is within range, this has a significant impact on resources at the UE, such as battery power, and can disrupt any existing services that might be running. The proposed method determines the probability of the UE being within range of a preferred cell based on measurements already available to the UE or by the network. Additional measurements can then be made as required, and made with increasing frequency as the probability of being within range of the preferred cell increases.