The younger son of an established Hampshire gentry family, Jephson made his career in Ireland as ‘a very gallant and worthy captain’ in the regiment of the 3rd earl of Southampton.
The patent brought Jephson into collision with the interests of the up-and-coming royal favourite, George Villiers, marquess of Buckingham, who had procured a timber licence for his client, Henry Mitton. It may have been in the hope of smoothing over any opposition that Buckingham vouched for Jephson in a suit in Chancery in England at around this time, asking the lord chancellor, Sir Francis Bacon* to ‘take notice of him [Jephson] as a gentleman whom for his worth and merits I much respect, and have such consideration of his cause as the justness thereof shall deserve’.
Jephson was returned for Hampshire at the general election of 1620 with the support of his friend and one-time commanding officer, the 3rd earl of Southampton, another opponent of Buckingham. He took lodgings in Great Turnstile, near his patron’s town house, and visited him to discuss their strategy of attack.
Jephson did not launch his assault on Buckingham until after the Easter break. On 26 Apr. he opened a debate on Ireland with a carefully prepared speech, recalling the vast expenditure of blood and treasure in the conquest of that country and the failure to convert the natives from popery.
Four days later James replied testily that he had taken notice of the abuses in Ireland, but was ‘the more stirred’ that Jephson, an Irish privy councillor, had not drawn his attention to these grievances before making his speech, since he would always be ready to listen.
In religion Jephson tended towards puritanism, something his enemy Grandison later lamented when Jephson was included on the commission to investigate Irish affairs.
Although he remained silent during the main debates on monopolies and the decay of trade, on 18 Apr. Jephson spoke against a proposed ban on tobacco imports because of the effect it would have on Virginia, drawing a parallel with other imported luxuries, such as wine.
In the second sitting, during the debate on foreign policy of 28 Nov., Jephson emphasized religion as the key motive for war, warning that ‘if the Protestants of France be destroyed, if the Low Countries, what next but this island? And Poland, when it hath peace with the Turk, will aid [the King of Spain]’. He advocated an alliance with the United Provinces against Spain, claiming that if James sent over an army of 10,000 men, receiving four Dutch towns as security for the cost of the war, he could safeguard the Protestant religion and put an end to piracy without himself incurring any expense.
In the summer of 1622 Jephson served on the commission sent to survey the state of Ireland, but his departure was delayed and by the time he arrived Grandison had already been recalled; his contribution to the commission was in fact minimal, and he was probably not paid for his service.
In the wake of the prince’s disappointment in Madrid, Jephson was more convinced than ever of the need for military action against Spain. In 1624, therefore, he stood for the Hampshire borough of Petersfield, 12 miles south of Froyle, perhaps with the support of Sir John Hippisley*, with whom he had served in Spain. On 23 Feb. 1624 he suggested that James Ussher, then bishop of Meath, should preach, but the House was informed that he wished to be excused.
Jephson was devastated by the death of his first wife in July 1624.
Jephson does not seem to have stood for Parliament in 1626. He may have been in Ireland, since his name appears on a list of Irish pensioners drawn up in that year.
After the dissolution Jephson obtained a licence to export 2,000 quarters of wheat to Ireland to relieve the shortage there.
