I've been wondering what 'lawful purpose' BoJo had for wearing that uniform:
"Any person who, not being a member of a police force or special constable, has in his possession any article of police uniform shall, unless he proves that he obtained possession of that article lawfully and has possession of it for a lawful purpose, be guilty of an offence and liable on summary conviction to a fine not exceeding level 1 on the standard scale."
[s. 90(3), Police Act 1996].