A communications device establishes a communications context for communicating data packets using a packet communications bearer from the communications device via mobile communications network in a connected state and releases communications context when in an idle state. A controller is configured in combination with a receiver to receive signalling information providing an indication of one or more functions performed by at least one of the receiver, a transmitter, or the controller which can be changed in a power saving state, and when in either the idle state or the connected state, to enter the power saving state in which the one or more of the operations performed by at least one of the receiver, the transmitter, or the controller are changed in accordance with the indication of the changed functions received in the signalling information from the mobile communications network.