A mobile communications system is proposed in which a two stage procedure is used for setting up Radio Bearers within a mobile communications device and UTRAN. In the first stage, both the mobile device and UTRAN perform ciphering based on an old Start value. In the second stage, the mobile device and UTRAN perform ciphering based on a new Start value. In this way, data communication using the Radio Bearers can start without waiting for the mobile device to confirm completion of the setup procedure.