The book I read is The Englishman's Room, by Alvide Lees-Milne and Derry Moore, published in 1986, ISBN 0 88162 214 1, first edition. I think the metadata for this book on Goodreads is wrong, because I see some reviews mentioning an edition with Benedict Cumberbatch on the cover, with a different title, and he was only ten years old in 1986.
Anyway. This book is a lovely journey. Each featured man discusses his day room, his den, his library, his man-cave before the term man-cave was ever conceived...how it came to be, and what it means to him to have this space to himself. These gentlemen are all clearly intelligent and creative, and it's a delight. So many said, "I don't even have a telephone in here." and isn't that just what we need, today? A quiet getaway room where one can sit and read, write, paint, draw, be? We should all be so lucky to have such.