John Buchan must have heard it in South Africa, from the Dutch for harnessing horses to a vehicle. As a metaphor, it was used by Kipling in a 1914 magazine article, a year before it was given wider currency by Buchan in his masterly novel, whose usage does not figure in the OED. It would be an erudite pun on spick and span for a firm of house cleaners.Reuse content
TO INSPAN somebody sounds like management-speak ("we've inspanned consultants to report back on the parameters of this project" - some people get paid for writing that sort of stuff all day long). In fact, it was used by Hannay in The Thirty-Nine Steps. He says of Paddock, "I had inspanned him as my servant as soon as I got to England. He had about as much gift of the gab as a hippopotamus."