knight of the post

Suggesting that such a person would be familiar with the whipping-post or pillory.

knight of the post (plural knights of the post)

1. (obsolete, idiomatic) A known perjurer; a professional false witness.
   • 1662, [Samuel Butler], “[The First Part of Hudibras]”, in Hudibras. The First and Second Parts. […], London: […] John Martyn and Henry Herringman, […], published 1678, →OCLC; republished in A[lfred] R[ayney] Waller, editor, Hudibras: Written in the Time of the Late Wars, Cambridge: University Press, 1905, →OCLC, canto I:

     […] But with more lucky hit than those
     That use to make the stars depose,
     Like knights o' th' post, and falsely charge
     Upon themselves what others forge;
     As if they were consenting to
     All mischief in the world men do […]

   • 1751, [Tobias] Smollett, The Adventures of Peregrine Pickle […], volumes (please specify |volume=I to IV), London: Harrison and Co., […], →OCLC:

     [T]he fugitive had been cajoled by a certain knight of the post, who undertook to manage the thousand pounds in such a manner, as would, in a very little time, make him perfectly independent […] .

   • 1592, Thomas Nashe, Pierce Penniless:

     A knight of the post […] quoth he, for so I am termed; a fellow that will swear you anything for twelve pence.