In Britain and beyond, health services are desperately seeking blood donors. But could science help ease the crisis? This week scientists have taken a step closer to being able to convert blood from one type to another, which would allow donations to be used more efficiently and effectively. Plus an immersive D-Day simulation, and analysing a weight-loss faux pas.Olly Mann and The Week delve behind the headlines and debate what really matters from the past seven days. With Harriet Marsden, Arion McNicoll and Suchandrika Chakrabarti