Thanks for that comprehensive reply Brian
Funnily enough I have got a facsimile copy of the Liddel book, but I wouldn't have noticed that if you hadn't said.
From there I thought it was worth looking at the official "Regulations & Instructions" - the edition I have here is 1790 - but I couldn't see anything in there about maintaining letter books (either in or out).
BUT I then found a similar book to Liddel's (by James Roddam Tate) dated 1840 and it looks from that as if the maintenance of a Letter Book for letters both in and out did later become part of the official Naval Instructions. See below.
During Nelson's career it certainly looks as if there was no requirement to submit the Letter Books to the Admiralty as there are a number of Letter Books at Monmouth. I have never seen these but it has got me really intrigued now!

Just to see the format of them, whether they included letters both in and out. etc. etc. If anyone on here has consulted these letter books at Monmouth please tell us all about them!
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