A mobile communications system including: at least one base station configured to communicate data to/from different terminal devices via respective of plural logically separate carriers of a wireless access interface; first and second terminal devices operable to camp-on to first and second carriers of plural carriers and to subsequently communicate data with the at least one base station via the first and second carriers. The first and second carriers support compatible synchronization signalling such that the first and second terminal devices both can synchronize with the first and second carriers to begin a camp-on procedure. Following synchronization with one of the first or second carriers to begin the camp-on procedure, the second terminal device is configured to determine whether or not to continue with the camp-on procedure in dependence on an aspect of physical layer signalling associated with a control channel of the carrier with which it has synchronized.