The investigators have developed and assessed the feasibility of performing whole--‐body multi--‐parametric MRI for staging metastatic disease. The investigators hypothesize that a whole body multi--‐parametric MRI will be more sensitive and specific than conventional imaging staging for detection of metastatic disease in patients with biochemical failure following local therapies. Investigators therefore propose a comparative trial of conventional imaging verses whole--‐body multi--‐parametric MRI within this population of men. The investigators would further like to explore whether heterogeneity between metastases of multi--‐parametric MRI signals can predict men unlikely to respond to ADT. The investigators aim to enhance the main study by exploratory work on exosome, pathway and genomic analysis, the results of which could lead to complimentary imaging / non--‐imaging biomarker combinations of clinical utility for patient stratification. Finally the investigators will perform a health economic analysis to assess the cost--‐effectiveness of whole--‐body multi--‐parametric MRI for metastatic disease staging compared with conventional staging with computed tomography and bone--‐scans.