maybe to prevent being identified? If the UK is broadening its powers to silence protesters like this, even being photographed as part of a movement of quote unquote “violence, hatred or intolerance” could be enough to face fines, arrest, or other social consequences.
I wish I could find more data on this subject going back to the early 20th century, all I could find was US defense spending. Info like this is a lot more useful with historical precedents to compare it to.