I'm not surprised it's missing from your dusty old law books. It refers to a letter received the satirical magazine Private Eyefrom an eminent firm of solicitors acting for a Mr Arkell. He was complaining about a story and was pursuing damages for defamation. The solicitors said the amount of damages and legal costs would be governed by the nature of Private Eye's reply.
The editor wrote back:
Dear Sirs
We acknowledge your letter referring to Mr J Arkell.
We note that Mr Arkell's attitude to damages will be governed by the nature of our reply and would therefore be grateful if you could inform us what his attitude to damages would be were he to learn that the nature of our reply is as follows: F*** off.
No more was ever heard from Mr Arkell.
Arkell's response is, therefore, a somewhat curt and negative one.