Very Cool! Where did you find it?

Nice. As Jlong pointed out, 12/6 is definitely the "Publication Price", not a date.

Yes you may be right, the part is a bit faded so cant be sure. Final book price was 13/6, maybe changed mind on pricing?
Its a coincidence it ties in with being sent to Tolkien on the 13th June as well.
A odd copy for sure , will try and find out more

It does say "price" on the brown cover. That part is not fully faded on my copy (though the word before price is - I think it is "Published".

There is also a paper insert which cleary states "About 12s 6d. net"

Interestingly, the proof jacket has a price of 13s 6d.

I like this "Specially Recommended for Libraries" stamp - a mark of excellence :)

Solved between our copies. Mine hasn't git the slip on it.
I have been told the seller i brought from worked for George Allen and there was only 10 copies? Just tryimg to get some more time info on this. Will post if anything comes to light.