Patients will be randomised (1:2 ratio) to a control and intervention arm. Patients in the control arm will receive best current practice of surgery at 6-8 weeks after CRT and then a standard course of chemotherapy. Patients in the intervention arm will receive a treatment plan according to their response to CRT, assessed using the mrTRG. Patients who have a good response to CRT will defer surgery until the cancer stops reducing in size or avoid surgery altogether if the cancer cannot be detected with repeat scans and assessments. Patients who have a poor response to CRT will have additional pre-operative chemotherapy. The investigators will be able to see if this reduces the size of the tumour further, before a decision is made about proceeding to surgery, and if this lowers the risk of the tumour spreading.