Deputy CMO Professor Jonathan Van-Tam clarifies: "There is no evidence that general wearing of face masks by the public who are well affects the spread of disease in our society."
In my little neck of the medical woods, thyroid disease, we forever read "there is no evidence that ..." with the target very often being the medicine liothyronine (T3).
What is meant is that no-one has yet run a properly designed trial of sufficient size to count as a controlled trial. There is evidence in every direction - just not evidence as they know it, Jim.
Indeed, until the 1960s, the only medicine available contained T3 and was used from the late 19th century until the very early 1980s in the UK. There really is actually no evidence,
in their terms, that NOT having any T3 is acceptable.
I suspect the same sort of word manipulation.
They answer should be that if there is no evidence, and in particular no evidence that it is a bad thing to do, go ahead, wear a mask. Give us advice on how to ensure that our home-made masks are as good as possible and how to keep them hygienic. If in doubt, try to choose the safest option.