Green’s Dictionary of Slang

(UK Und.) a supposedly infallible scheme.

1812		Vaux Vocab. of the Flash Lang. in McLachlan (1964) 238: drummond: any scheme or project considered to be infallible, or any event which is deemed inevitably certain, is declared to be a Drummond; meaning, it is as sure as the credit of that respectable banking-house, Drummond and Co.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.