Thistlewood, Arthur, 1770—1820, British conspirator. He acquired revolutionary views while traveling in France and America and, after his return to England, joined the revolutionary Spencean Society (see Spence, Thomas) in London. In 1816 he organized a public meeting at Spa Fields, at which a revolution was to be started. However, the meeting was easily dispersed, and Thistlewood was arrested and narrowly escaped conviction for treason. A year later he was imprisoned for challenging Lord Sidmouth, the home secretary, to a duel. Upon his release (1819) Thistlewood, dissatisfied with the milder efforts of his colleagues, plotted the assassination of cabinet members at a cabinet dinner. The government, apprised of the conspiracy, surprised the plotters at their arsenal in a Cato Street loft. Thistlewood was subsequently convicted of treason and executed for his part in what is known as the Cato Street Conspiracy