Perceval was born into the ruling elite of the United Kingdom in 1803. His father Spencer Perceval, a son of the 2nd Earl of Egmont, was a lawyer and politician who became prime minister in 1809. Perceval was the tenth of thirteen children (of whom twelve survived infancy). When Perceval was nine his father was shot dead in the lobby of the House of Commons. The assassin, John Bellingham, was a merchant with a grievance against the government and was widely believed to be insane (although at his trial he pleaded injustice rather than insanity and was executed). Press reports described how one of the Perceval boys had been in Parliament and had seen his father's body moments after the shooting, and a psychoanalyst has suggested that this child was Perceval and that witnessing the scene may have been the cause of his subsequent regressive experience. Perceval himself recognised the loss of his father - along with mercury poisoning and over-study of religion - as a contributory factor in his breakdown.