A method of operating a terminal device in a wireless telecommunications system that supports a connected mode of operation in which terminal devices receive a type user-plane data from the network infrastructure equipment using primary and/or secondary component carriers operating on different frequency bands and an idle mode of operation in which terminal devices do not receive that type of user-plane data from the network infrastructure equipment. The method includes: establishing a measurement configuration making measurements of radio channel conditions for radio resources within the second frequency band; making measurement of radio channel conditions for radio resources within the second frequency band in accordance with the measurement configuration while the terminal device is operating in the idle mode; determining if the measurement of radio channel conditions meets a trigger criterion, and if so, transmitting a measurement report to the network infrastructure equipment to indicate the trigger criterion has been met.