Jemmy Twitcher. A name given to John, Lord Sandwich (1718-1792), noted for his liaison with Miss Ray, who was shot by the Rev. “Captain” Hackman out of jealousy. His lordship's shambling gait is memorialised in the Heroic Epistle.
“See Jemmy Twitcher shambles- stop, stop thief!”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894