"The shoes are said to have got that name because they were often left outside hotel rooms, ostensibly to be cleaned, as an easily identifiable signal that hanky-panky should be assumed to be taking place within. This was because the only permitted cause for divorce at the time was adultery by one partner. For a couple to arrange a divorce in an amicable way, one member - it was commonly the man - had to be caught in flagrante with another woman. A minor industry grew up in which housemaids in hotels augmented their meagre wages by giving evidence of having found the supposedly adulterous couple in bed together."
A partial extract from the World Wide Words e-newsletter 1st March 2008 (archives here)
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Picture credit.....because apparently you can still buy them (though I guess Renown 1886 Online Outfitters aren't necessarily going for the same market share these days as they've introduced an extra "r" into the spelling, co-respondent thereby becoming correspondent......which shifts the meaning from the threateningly "legal" to the much more acceptable "literary") And a paltry £135 a pair.....but, on the upside, there's two colourways to choose from guys!