He may have deliberately worn the uniform (and I absolutely understand the annoyance of those who have worked and sacrificed to earn the right to do that)
Not just once but repeatedly. Unlike dressing up in a long gown and tiara, it is unlawful.
If any person not serving in Her Majesty’s Naval or Military Forces wears 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, in such a manner or under such circumstances as to be likely to bring contempt upon that uniform, or employs any other person so to wear that uniform or dress, he shall be liable on summary conviction to a fine not exceeding [level 3 on the standard scale], or to imprisonment for a term not exceeding one month.
He is not the only one, there have been a few others in recent years.
No, it did not cause danger to others, it's sad that he needs to do that.
Worrying that such a fantasist was a teacher too.