To paraphrase P.T. Barnum, no one ever lost money overestimating the research of Martin Gilbert.
Ever since the producers of "The Wilderness Years" took liberties by suggesting Churchill's key 1930s informant, Ralph Wigram, was a suicide, it has been broadly accepted as fact. Indeed recently another myth was layered on to this one: that Ralph's parents didn't attend his funeral in Sussex because suicide was proscribed by the Church.
Hugh Axton put that canard to rest in Finest Hour 163 page 62: "On the morning of his funeral Wigram's parents were attending a memorial service for him at Landkey Parish Church near Barnstaple, Devon. Ralph was brought up in the area and many family friends attended who could not have journeyed to Sussex and returned home at short notice in winter."
William Manchester was a peerless stylist but had an unfortunate tic about the seamy and judgmental (there is nothing to suggest Churchill was, as he says, "less than generous" toward Wigram, in fact quite the opposite). And his footnotes are often, as in this case, a mare's nest.
On Wigram in The Last Lion, vol. 2, Alone 1932-1940 (UK title The Caged Lion) Manchester (193) quotes the biographer Henry Pelling: "depression overtook him and he committed suicide." But Manchester's footnote leads not to Pelling's Churchill (1974) but to Vansittart's The Mist Procession, Churchill's The Gathering Storm and Gilbert's The Wilderness Years—none of which contain any reference to suicide.
In Pelling's book the comment is footnoted The Gathering Storm pages 73 and 178 (English edition 1948). But Wigram is not mentioned there. Churchill does recount Wigram's death (155) but does not call it a suicide. Indeed in Gilbert's document volume we find WSC saying to his wife that Ralph "died in his wife's arms," which doesn't strike one as likely in the case of suicides.
So the question is, where did Pelling get this impression? Until a valid source is offered, the answer to anyone spouting this old story is the tried and true one: "Prove it."