Free registration by the censor

[gmark]

Last weekend I was shown this cover and asked what I thought of it.
From Helsinki 8 December 1917, paid 4k (the basic foreign printed paper rate) to Leeds.
It was censored at Helsinki the next day (Moxter type S21, No.145) partly covered by the British censor's label.
It was in London on 24 January 1918 where is was censored and registered at the censorship (the London PC label ).
The initials in the circular POSTAL CENSORSHIP handstamp are ERFG = E R FitzGerald the head of the Registered Section.
It arrived in Leeds on 25 Jan (the postmark is over the 4k stamp).
I have never seen free registration by the London censors - has anyone seen such a cover before?
Your comments will be welcome.
Graham Mark

[mozzerb]

Old post I know, but at a guess this was a case of compulsory registration -- i.e. the rules by which unregistered letters that were found to have items of value inside were officially registered? Most commonly this was because said items were obvious (coins), but it could be because valuables were found inside the letters when they were opened. The usual case when that happened was returned mail, but it would make sense that if the censors found something valuable in a letter they would register it, if only to cover themselves.