 Readily found in Tewkesbury's shops and the local mustard company 'The Tewkesbury Mustard Company' online.There is some evidence that “Tewkesbury Mustard” came to be used as slang for incendiary 'fire-balls', a usage referred to in David Hume's "History of England", in which he describes the rumour that the Great Fire of London was started by foreign arsonists trained by Jesuits "and the whole plan of operations was so concerted, that precautions were taken by the Jesuits to vary their measures, according to the variation of the wind.Fire-balls were familiarly called among them Tewkesbury mustard pills".