Arthur Thistlewood 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.