 PLUMMB is an phase I trial to investigate the safety, tolerability and effectiveness of an immunotherapy drug called Pembrolizumab used in combination with radiotherapy. The study will also investigate two different doses of pembrolizumab, starting at 100mg through an intravenous drip and increasing to 200mg for the next cohort of patients, if the first dose is well tolerated. The patients suitable for this study will be: Group A those with locally advanced bladder cancer or Group B patients whose cancer has spread from the bladder metastatic bladder cancer. 