A method of operating a terminal device (406, 408) in a wireless telecommunications system for communicating with network infrastructure equipment in accordance with a first radio access technology on a primary cell supporting a primary component carrier on radio resources within a first frequency band and a secondary cell supporting a secondary component carrier on radio resources within a second frequency band, wherein the terminal device is also operable to use radio resources within the second frequency band for communicating in accordance with a second radio access technology, wherein the method comprises: receiving from the network infrastructure equipment an indication of a configuration of radio resources within the second frequency band for use by the terminal device for communications with the network infrastructure equipment in accordance with the first radio access technology; establishing a configuration of radio resources within the second frequency band for use by the terminal device for communications in accordance with the second radio access technology; determining if there is an overlap in the radio resources configured for use by the terminal device for communications in accordance with the first radio access technology and the radio resources configured for use by the terminal device for communications in accordance with the second radio access technology, and if so, transmitting signalling to the network infrastructure equipment to indicate there is an overlap to indicate a potential for inter-frequency interference arising between different frequencies associated with different radio access technologies supported by the terminal device using an inter-frequency in-device coexistence, IDC, message having a predefined format, and wherein the signalling transmitted to the network infrastructure equipment to indicate there is an overlap conforms to the inter-frequency in-device coexistence, IDC, message format. receiving from the network infrastructure equipment an indication of a configuration of radio resources within the second frequency band for use by the terminal device for communications with the network infrastructure equipment in accordance with the first radio access technology; establishing a configuration of radio resources within the second frequency band for use by the terminal device for communications in accordance with the second radio access technology; determining if there is an overlap in the radio resources configured for use by the terminal device for communications in accordance with the first radio access technology and the radio resources configured for use by the terminal device for communications in accordance with the second radio access technology, and if so, transmitting signalling to the network infrastructure equipment to indicate there is an overlap to indicate a potential for inter-frequency interference arising between different frequencies associated with different radio access technologies supported by the terminal device using an inter-frequency in-device coexistence, IDC, message having a predefined format, and wherein the signalling transmitted to the network infrastructure equipment to indicate there is an overlap conforms to the inter-frequency in-device coexistence, IDC, message format.