A method of operating a wireless telecommunications system for handing over a terminal device from a source network infrastructure element to a target network infrastructure element, the method being carried out by a wireless telecommunications system which supports communications in accordance with LTE and NR, and which comprises the source network infrastructure element and the target network infrastructure element, wherein the target network infrastructure element is operable to communicate with the terminal device in accordance with LTE and the source network infrastructure element communicates with the terminal device in accordance with LTE and NR, and wherein the method comprises: establishing, at the source network infrastructure element, that the terminal device should be handed over from the source network infrastructure element to the target network infrastructure element; transmitting, from the source network infrastructure element to the target network infrastructure element, a handover request message comprising an indication of a source radio resource configuration for communications between the source network infrastructure element and the terminal device in accordance with LTE and an indication of a source radio resource configuration for communications between the source network infrastructure element and the terminal device in accordance with NR which includes NR RLC-config, NR MAC-config, and NR PHY-config; transmitting, from the target network infrastructure element to the source network infrastructure element, a handover request acknowledgement message comprising an indication of a target radio resource configuration for communications between the target network infrastructure element and the terminal device in accordance with LTE, further comprising the target network infrastructure element determining from the handover request message if there is an aspect of the source configuration of the terminal device which relates to NR which is not supported by the target network infrastructure element, and wherein the indication of the target radio resource configuration comprises a full LTE radio resource configuration for communications between the target network infrastructure element and the terminal device using LTE if the target network infrastructure element determines from the handover request message that there is an aspect of the source configuration of the terminal device which relates to NR which is not supported by the target network infrastructure element, or otherwise the indication of the target radio resource configuration comprises a delta configuration; and transmitting, from the source network infrastructure element to the terminal device, a radio resource control reconfiguration message comprising an indication of the target radio resource configuration, wherein the source network infrastructure element communicates with the terminal device using a radio bearer supported by a first layer-2 protocol stack for communications in accordance with LTE and a second layer 2-protocol stack for communications in accordance with NR. establishing, at the source network infrastructure element, that the terminal device should be handed over from the source network infrastructure element to the target network infrastructure element; transmitting, from the source network infrastructure element to the target network infrastructure element, a handover request message comprising an indication of a source radio resource configuration for communications between the source network infrastructure element and the terminal device in accordance with LTE and an indication of a source radio resource configuration for communications between the source network infrastructure element and the terminal device in accordance with NR which includes NR RLC-config, NR MAC-config, and NR PHY-config; transmitting, from the target network infrastructure element to the source network infrastructure element, a handover request acknowledgement message comprising an indication of a target radio resource configuration for communications between the target network infrastructure element and the terminal device in accordance with LTE, further comprising the target network infrastructure element determining from the handover request message if there is an aspect of the source configuration of the terminal device which relates to NR which is not supported by the target network infrastructure element, and wherein the indication of the target radio resource configuration comprises a full LTE radio resource configuration for communications between the target network infrastructure element and the terminal device using LTE if the target network infrastructure element determines from the handover request message that there is an aspect of the source configuration of the terminal device which relates to NR which is not supported by the target network infrastructure element, or otherwise the indication of the target radio resource configuration comprises a delta configuration; and transmitting, from the source network infrastructure element to the terminal device, a radio resource control reconfiguration message comprising an indication of the target radio resource configuration, wherein the source network infrastructure element communicates with the terminal device using a radio bearer supported by a first layer-2 protocol stack for communications in accordance with LTE and a second layer 2-protocol stack for communications in accordance with NR.