 2. Phase 1 trial of Pembrolizumab: Patients will be carefully monitored for toxicity throughout the trial. A phase I trial has already been conducted to determine the maximum tolerated dose MTD of pembrolizumab in bladder cancer. To date no MTD has been defined and the maximum dose tested showed acceptable toxicity and positive effects on reducing tumour size. This study will assess two dose levels, 100mg and 200mg. Dose escalation will only occur if the first group on 100mg have shown no signs of unacceptable toxicity at 11 weeks after completing radiotherapy. 