A 58-year-old man with a history of type 2 diabetes mellitus and hypertension presents to his GP with a 3-month history of intermittent pain in his calves on walking approximately 200 metres. The pain is relieved by rest. His ABPI is 0.7 in the right leg and 0.65 in the left leg. He is a current smoker of 20 cigarettes per day. What is the most appropriate initial advice regarding exercise, according to NICE CG147?