Does anyone know the truth about face masks?

In recent days, more supportive noises have been made by those on the top of government about the wearing of face masks indoors, especially in shops. Scotland has already made it compulsory. But it wasn’t long ago when the government was saying that face masks may even harm efforts to control the virus. So does anyone know the truth about face masks? Katy Balls talks to James Forsyth and Fraser Nelson.