Phil,
I am sorry, but with all do respect. I never seen the document, from any government without department registration number. Main reason for that, farther documentation, will not be able to reference it.
Second warning point for forgery, British documentation, memos, etc should contains FROM/TO field. Reason for that, British MI, I think large organization, even back to 1916/1917 period of time. If memo - department wide, it should contain FROM field for authorization reason.
And again, I will repeat, this is not a musketeer time, they didn't had to ride the horse, in order to deliver the message to the queen. Communication, was done by telegraph, especially just basic translation/report of the local news.