Diabetic patients will be enrolled into this trial due to the frequency of diabetic patients with renal failure and the contributing role of diabetes in small vessel disease leading to critical ischaemia. The distinction between painful diabetic neuropathy and digital critical ischaemia can be difficult to make clinically and it may be that a small proportion of patients recruited for this study also have an element of diabetic neuropathy in addition to their critical ischaemia. In view of the concern with ulceration of the feet in diabetics treated with Qutenza, patients with diabetic neuropathy causing a loss of sensation will be excluded from having their feet treated.