A method of communicating data in a wireless telecommunications system, the system comprising a base station (404, 720, 820) and one or more terminals (406, 408, 710, 810) operable to communicate via a wireless interface and in accordance with a mobile communication protocol, the wireless interface being provided by at least a first component carrier within a first frequency band and a second component carrier within a second frequency band, wherein the method comprises: transmitting a link control layer Packet Data Unit, PDU, from a link control module (712, 812) to an access control layer module (711, 811) for transmission, the link control layer being at a higher layer than the access control layer; transmitting first access control layer data using resources allocated within the first component carrier, wherein the first access control layer data corresponds to the PDU; maintaining at the access control module information indicating transmission of the first access control layer data on the first component carrier; identifying that transmission of data for the PDU has been unsuccessful; and upon identification that transmission of data for the PDU has been unsuccessful, the link control module re-transmitting to the access layer control module the PDU and transmitting a retransmission indicator indicating that the PDU relates to retransmission, said retransmission indicator including at least one of: an indication that the first component carrier within the first frequency band was used for previously attempting to transmit the PDU and an indication that the second component carrier within the second frequency band is to be used for re-transmitting the PDU; and upon receipt of the PDU and of the retransmission indicator at the access control layer module, transmitting the second access control layer data using resources allocated within the second component carrier, wherein the first frequency band comprises radio resources which have not been licensed for exclusive use by the wireless telecommunications system, and the second frequency band comprises radio resources which have been licensed for exclusive use by the wireless telecommunications system. transmitting a link control layer Packet Data Unit, PDU, from a link control module (712, 812) to an access control layer module (711, 811) for transmission, the link control layer being at a higher layer than the access control layer; transmitting first access control layer data using resources allocated within the first component carrier, wherein the first access control layer data corresponds to the PDU; maintaining at the access control module information indicating transmission of the first access control layer data on the first component carrier; identifying that transmission of data for the PDU has been unsuccessful; and upon identification that transmission of data for the PDU has been unsuccessful, the link control module re-transmitting to the access layer control module the PDU and transmitting a retransmission indicator indicating that the PDU relates to retransmission, said retransmission indicator including at least one of: an indication that the first component carrier within the first frequency band was used for previously attempting to transmit the PDU and an indication that the second component carrier within the second frequency band is to be used for re-transmitting the PDU; and upon receipt of the PDU and of the retransmission indicator at the access control layer module, transmitting the second access control layer data using resources allocated within the second component carrier, wherein the first frequency band comprises radio resources which have not been licensed for exclusive use by the wireless telecommunications system, and the second frequency band comprises radio resources which have been licensed for exclusive use by the wireless telecommunications system.