The last time that David Miliband cried was when he realised that he and his wife, Louise, could not have children. “It wasn’t a one-off event,” he says. “It was a long process. We didn’t just go to the doctor and find out, it took years. It was very drawn out and difficult but there was a moment when we realised that we had reached the end of the line and we weren’t going to give birth to our children.”