My spanner in the works is that I have recently seen Admiralty Civil Police buttons in an old collection on the internet. They were chrome R.N. Petty Officers' buttons both KC and QC.
I had the plain, no rim, KC/QC over foul anchor as Admiralty Constabulary.
Wikipedia has an article on this force:
https://en.wikipedia.org/wiki/Admiralty_Constabulary
The force is now known as Ministry of Defence Police
Wikipedia has this on the Royal Navy Police:
https://en.wikipedia.org/wiki/Royal_Navy_Police