Richard Dehan The Dop Doctor

The Dop Doctor is a novel written by Clotilde Graves in 1911 under the pen name of Richard Dehan, although she was already known as a writer (chiefly for the theatre) under her own name.

The story hinges around a drunken and disgraced medic who eventually makes his way to South Africa where he redeems his honour at the Siege of Mafeking. Albert Gérard, in his European-language writing in Sub Saharan Africa, regards the book's description of the siege of Mafeking "as a heroic justification of British Imperial strategy and the vindication of a belief in the righteousness and superiority of the British cause. The Dop Doctor contains pro-Jingo arguments of the type which offers the stereotypical portrait of the Boer as backward and despicably primitive, and the black man as a shadow figure behind the civilizing foreground, an appendage of an argument over what to do with his labour". The incidentials of the novel, however, should not distract from its pimary objective of tracing a story of redemption through expiatory suffering and kenosis, a subject much explored by writers, in several European languages, connected with the literary renouveau catholique movement. It was made into a film in 1915 by Fred Paul. The film gave considerable offence in South Africa due to the harsh portrayal of English and Dutch characters. It was eventually banned under the Defence of the Realm Act. Wikipedia

We must assume that Lowry read the book as he makes reference to a drink and comments about the drink only found in this book to date:

"Dop," being the native name for the cheapest and most villainous of Cape brandies, has come to signify alcoholic drinks in general to men of many nations dwelling under the subtropical South African sun. Thus, apple-brandy, and peach liqueur, "Old Squareface," in the squat, four-sided bottles beloved no less by Dutchman and Afrikander, American and Briton, Paddy from Cork, and Heinrich from the German Fatherland, than by John Chinkey—in default of arrack—and the swart and woolly-headed descendant of Ham, may be signified under the all-embracing designation." (The Dop Doctor Pg. 99).

Lowry refers to Cape Dopp in his short story 'Seductio ad Absurdum'; "And it wasn't wine at all but Cape Dopp, wot we call Cape Dopp— raw spirit gawd blimey. Why, do you know, we all went mad, mad, and they had to tie Deaffy up to the bullock post." (Pg. 9) and "Fellers used to keep em as pets and make em drunk on Cape Dopp." (Pg. 9); these lines are repeated in his first novel Ultramarine (Pgs.127-128).  Lowry also uses the phrase 'Old Squareface' in Ultramarine when the quartermaster on board Oedipus Tyrannus asks Dana to his cabin for a drink; "Come along to my room and have a slice of old squareface."  Pg. 37