According to SFE3, "Although a few copies of the 1918 version exist [...], this first printing was withdrawn after an offended newspaper magnate (possibly Lord Beaverbrook) threatened to sue for libel: the two passages in question portray a newspaper proprietor attempting political blackmail. With some (rather mild) paragraphs rewritten, the novel was republished the next year, and bibliographies usually date the book 1919."
A first edition of this text is viewable online at TIA
The primary foreword of the book (shown in the table of contents) has a date of April 1918.
A tipped in / pasted in foreword on the front endpaper has a date of March 1919.
According to SFE3, "Although a few copies of the 1918 version exist [...] first printing was withdrawn after an offended newspaper magnate (possibly Lord Beaverbrook) threatened to sue for libel: the two passages in question portray a newspaper proprietor attempting political blackmail. With some (rather mild) paragraphs rewritten, the novel was republished the next year, and bibliographies usually date the book 1919."
Bleiler78 and the LOC agree on a 1919 publication date, while Worldcat shows 1918.
1919 is used for the publication date, based on the pasted foreword shown at TIA.
Price from "Constable's New Fiction" advertisement seen on Google Books in The Publishers' Circular and Booksellers' Record, Volume 110 (January to June, 1919).
