With data on the Covid-19 pandemic changing shape with every new outbreak and new mutation, it's a complex task to make sense of where the story of the virus will head next. David Spiegelhalter is chair of the Winton Centre for Risk and Evidence Communication at Cambridge University and an expert on crunching figures in order to understand successes and failures. His new book Covid by Numbers, co-written with Anthony Masters, seeks to shine a spotlight on the UK's handling of the pandemic. In this episode he speaks with the virologist and host of The Naked Scientist podcast Dr Chris Smith.