I can't say whether this is the actual origin, but in 1929 this praise from Christie appeared on the back panel of a dust jacket to a Knopf reprint edition of Trent's Last Case. However, Christie's praise, in contrast with the cheese, did not stand alone. Nine other British crime writers were blurbed on the back panel, as you can see below, under the heading "What your favorite authors say": It gives you a good roll call a some of the notables of British detective fiction in the late 1920s, when the Detection Club was cohering.
|see Facsimile Dust Jackets
Left Column, top to bottom
Trent's Last Case is a masterpiece of detective fiction.
Freeman Wills Crofts
I have read the book three times with an increased interest each time: one of the best detective stories extant.
J. J. Connington
Mr. Bentley's record is, as far as I know, without a parallel....a detective story which appeals to women as well as men. It does not date, it might have been written yesterday.
J. S. Fletcher
The very best and cleverest detective story I have read.
Right column, top to bottom
I suppose somebody might write a story as good as Trent's Last Case, but I have been waiting nearly twenty years for it to happen.
R. Austin Freeman
The literary workmanship is of a quality that must satisfy the most fastidious reader.
One of the three best detective stories ever written.
It is the one detective story of the present century which I am certain will go down in posterity as a classic. It is a masterpiece.
G. D. H. and M. I. Cole
The best detective story we have ever read.
Connington probably will be dinged for sexism, and, having written about him extensively in Masters of the "Humdrum" Mystery" I can't deny that he presents some issues in that regard, but in fact he was reflecting the wide perception at the time that true detective fiction (as opposed to shockers) appealed more to men than to women.
It was only until the rise in the 1930s of crime writers, often women, who put more emphasis on characterization and literary style (and dare I say love interest) that this perception (and arguably the reality) really changed. This development is something I discuss in Masters. (You'll notice only three of the ten blurbers are women.)
I originally came across this information when editing a Roger Ellis essay on J. S. Fletcher which was included in Mysteries Unlocked: Essays in Honor of Douglas G. Greene. Fletcher in the 1920s and early 1930s was one of the most people detective fiction authors in the world. All of the blurbers, incidentally, became founding members of the Detection Club, formed the next year in 1930, except for Fletcher and Edgar Wallace. Fletcher likely was considered too dodgy on the matter of "fair play" presentation of clues, while the Detection Club to some degree was created to distinguish true detective fiction from the "shockers" of Edgar Wallace and other crime writers of the palpitation school.
It was the blurb from Wallace, you'll notice, which appeared on the front of the dust jacket, indicating who really ruled the roost in those days. But it appears that Trent's Last Case managed to unite all British mystery writers. On this matter Crime Queens, Humdrums and Farceurs all concurred with the Titan of Thrills.
One question remains: Why did this list of blurbs appear on a book published by Knopf, an American publisher? (Their stable of authors included J. S. Fletcher and Dashiell Hammett.) Did the list appear first in Britain? Were these testimonials solicited and then edited? (Notice the ellipses in the Connington quotation.) Or had they already appeared in other sources and been assiduously collected by some Knopf editor? Mysteries remain for literary investigators!
Also, what were the other two best detective stories, according to Christie?
Also see The Boost of the Blurb: Death of a Beauty Queen (1935), by E. R. Punshon