In 1754 Henry Ingram, 7th Viscount Irwin, owned a majority of the burgages at Horsham and controlled both seats. On the death s.p. in 1778 of Charles, 9th and last Viscount, the property devolved upon his widow, who in 1780 and 1784 placed both seats at the disposal of Administration. In 1786 Charles, 11th Duke of Norfolk, lord of the manor of Horsham, began purchasing burgages with a view to challenging the Irwin interest, which he did at the general election of 1790.