He could well have been breaking Section 2 of the Uniforms Act 1894:
"It shall not be lawful for any person not serving in Her Majesty’s Military Forces to wear without Her Majesty’s permission the uniform of any of those forces, or any dress having the appearance or bearing any of the regimental or other distinctive marks of any such uniform: Provided that this enactment shall not prevent any persons from wearing any uniform or dress in the course of a stage play performed in a place duly licensed or authorised for the public performance of stage plays, or in the course of a music hall or circus performance, or in the course of any bona fide military representation."
Personally, I think common sense has a place in these matters.
(and I know I need to get out more)