Professor Sir Michael Marmot is interviewed by Kirsty Young for Desert Island Discs. He's an epidemiologist who has spent his career studying what the key factors are in leading a long and healthy life and how your income and post code can affect your longevity.

Professor of Epidemiology and Public Health and Director of the Institute of Health Equity at University College London, Sir Michael specialises in what are known as the social determinants of health: how where we are in the wealth and status pecking order directly influences our chances of illness, disease and lifespan. Why is it, for example, that in 2014 in the same British city the average life expectancy for a man in one post code will be 82 but just a few miles away it's 54?

His pioneering research is often at odds with wider societal concerns over what are known these days as lifestyle choices - like smoking, not taking any exercise or eating junk ... he says simply "what I contribute to the policy debate is that I bring evidence - I don't do the skulduggery of politics.".