How does the sporting notion of fairness cope with the complexities of gender identity? HARDtalk’s Stephen Sackur speaks to former champion British swimmer turned sports commentator Sharron Davies. Elite level sport is ruthlessly competitive. The best male and female athletes push hard against their physical limits in the quest for marginal gains. But what happens when athletes change gender - in particular when individuals born biologically male transition to female after puberty. Should they be allowed to compete as women?