MacGill returned to England in September 1915 and spent time ‘all dressed in blighty blue’ in the first Birmingham War Hospital at Ruberry Hill. In the following month he contributed to The Times fund-raising publication Red Cross Story Book and by February 1916 he was fit enough to appear in London Irish Rifles uniform at fund-raising evenings in London during which his wife read from his ‘Story of Loos’, which was to become a central part of The Great Push.His commitment to the war was reflected in The Red Horizon which opened simply:

TO THE LONDON IRISH

TO THE SPIR IT OF THOSE W HO FIGHT A ND TO THE M EMORY OF THOSE W HO H AV E PASSED AWAY THIS BOOK IS DEDICATED

MacGill remained in the London Irish Rifles and clearly enjoyed the companionship and sense of belonging that it provided. Although it is not possible to demonstrate this directly, the continuity of personnel between his pre- and post-Loos war writings suggest that he kept in touch with certain individuals with whom he had fought. He was seconded to the Army Intelligence Service, allegedly to curtail his writings on the war, which were deemed to be too critical, but MacGill's precise role in the years from 1916 to 1918 is impossible to establish. In retrospect he appears to have chafed at the restrictions imposed upon him by censorship, though whether this accurately reflects his thinking at the time cannot be said with confidence. In fact, although he was condemned by Richard Aldington for producing government propaganda, MacGill's writings about the war during this time are more complex and less obviously propagandistic than the work of other writers recruited by Charles Masterman, the head of the War Propaganda Bureau. For example, Arthur Conan Doyle's A Visit to Three Fronts, published in 1916, was the product of a government-funded enterprise and provided a very upbeat and sanitized view of the war that showed little understanding of the ordinary soldier. In contrast, MacGill continued to offer a nuanced ‘bottom-up’ view as his ongoing engagement with war continued.

MacGill's fund-raising activities and his public statements in late 1915/ early 1916 do not suggest that he was critical of or disillusioned with the war effort.