I was hoping for some recommendations on books on the following areas

History of George Allen publishers

I am not really aware of any books that deal with the history of George Allen before Sir Stanley Unwin bought the company, though there is a chapter in George Allen & Unwin: A Remembrancer.

Wellinghall provided the following book

From Swan Sonnenschein to George Allen & Unwin Ltd -
Mumby, F.A. & Frances H.S. Stallybrass (GA&U)

History of George Allen & Unwin publishers

The books that I currently have which deal with this area are:

The Truth about a Publisher - Sir Stanley Unwin (GA&U)
The Publishing Unwins - Philip Unwin (Heinemann)
Fifty Years with Father: A Relationship - David Unwin (GA&U)
George Allen & Unwin: A Remembrancer - Rayner Unwin (Merlin Unwin)

Wellinghall provided the following booklet

Sir Stanley Unwin: The Celebration of his 80th Birthday and Golden Wedding Day; with allusions to 50 years of George Allen & Unwin Ltd under his direction; 40 years on the Executive of The International Publishers Association; and 30 years on The British Council - Booklet

Findegil provided the following pamphlet

Fifty Years of Publishing Books That Matter - Unknown Author (GA&U)

and I would probably also include

The Truth about Publishing - Stanley Unwin (GA&U) though not dealing exclusively with George Allen & Unwin

History of Unwin Brothers printers

The Printing Unwins : a short history of Unwin brothers, the Gresham Press, 1826-1976 - Philip Unwin (GA&U)

Does anyone have any other recommendations?