The Return of the King.
2nd Edition, 7th Impression 1973.
George Allen & Unwin.
ISBN 0048230472.
Hardback in dustwrapper.
Hammond p.138.

In total 7 essentially similar impressions were issued before the dustwrapper design was changed again:

7th Impression 1973
8th Impression 1974
9th Impression 1978
10th Impression 1978
11th Impression 1980
12th Impression 1984
13th Impression 1985

Some copies have the ISBN for The Two Towers on the dustwrapper.

Some copies of the 7th Impression 1973 have been seen with the previous style of  dustwrapper.