Jeffery’s family (said to be Quakers) were involved in the Newfoundland trade from Poole and he was described as ‘opulent’. Nevertheless he informed the prime minister, 22 June 1786, in a letter of protest against proposed regulations affecting the trade, that ‘large fortunes have been made by it, and large fortunes lost’ and that the damage done to it by war was so great that ‘I will never risk ... in so large a way as I have done, and if I can but get a little notice of an approaching war sufficiently to draw in and wind up, depend on it I shall leave the trade to those who have no regard for themselves or their fortunes’. With reference to the president of the Board of Trade’s wishes ‘in destroying what he calls the monopoly’, he went on, ‘whatever opinion Mr Jenkinson might entertain of the great overgrown merchants it is to them the country stands indebted for the flourishing state of that trade’. He particularly objected to the stoppage of shipbuilding in Newfoundland proposed under the navigation bill: ‘I presume we can finish those on the stocks ... I have three and Mr [Benjamin] Lester has more ... my partner will else have to style himself an inhabitant of Newfoundland.’
Jeffery apparently did to some extent ‘draw in and wind up’, for soon afterwards he was established at a tasteful retreat near Poole and interesting himself in the affairs of the borough. He belonged to the faction opposed to the ministerialist Member Benjamin Lester, and to judge by an appeal to him from William Adam for a Poole subscription towards Fox’s debts in 1793, had shared the Whig views of the other Member Michael Angelo Taylor, who in 1794 described Jeffery as his agent. Taylor was amazed to discover that Jeffery had been in consultation with the Duke of Portland behind his back with a view to replacing him by a more popular candidate. While Jeffery denied any conspiracy or misrepresentation and offered to accept the duke’s nominee, he unabashedly offered his own services, wishing to be in Parliament (3 Oct. 1794). He also sought, as proof of his standing with government, a preference in the barracks contracts at Poole. By November 1795 he was accepted as candidate and confident of a quiet election by compromise.
Jeffery defended Pitt’s cavalry bill as a token of government’s exertions for home defence, 2 Nov. 1796.
Jeffery’s parliamentary career reached a sudden climax in May 1805 when he inaugurated a campaign against St. Vincent’s naval administration under Addington. He had joined the majority which censured Melville on 8 Apr. (and voted for his criminal prosecution on 12 June). On 2 May he announced that ‘the affairs of the navy were never worse conducted than during the administration of Earl St. Vincent: not only the navy, but the whole of the commercial community were loud in their complaints against it’. On 7 May he produced 18 resolutions to prove his point; then and on 10 May he protested that he ‘did not act through party motives’. He was however thwarted on 25 June, and on 1 July, describing St. Vincent as ‘the worst enemy this country ever had’, he promised to resume the matter next session. When he did so on 28 Jan. 1806, Pitt was dead, but he complained of delays in producing papers by the Admiralty and promised to abide by his accusations. St. Vincent alleged, 15 Mar. 1806, to John Markham, who defended him against the charges:
Mr Jeffery is in such desperate circumstances in every point of view, that he will go the whole length. It is strongly suspected that Sir Andre [Snape] Hamond is in collusion with him, and has given him a lucrative contract, drawn up in the name of Lenthorn, a creature of his.
He voted against the Grenville ministry on 3 Mar. and 30 Apr. 1806, having meanwhile (14 Apr.) asked them to fix a day for his indictment of St. Vincent. On 21 May, asked to postpone it once more, he named his charges as ‘misconduct, neglect and mismanagement’. At this stage, Jeffery was in consultation with Pitt’s friends, at least with Canning, who wished he would postpone the subject until Melville’s trial was over. But on 14 May he brought in 24 resolutions against St. Vincent for a committee of the House to consider. The Speaker criticized him for reading his speech and he admitted that he was ‘little acquainted with the forms of the House’; moreover, his complaints were refuted by Admiral Markham and Lord Howick. His reply ‘of great length’ was again castigated by the Speaker because he read it out and his motion was negatived without a division. As Fox followed this with a motion approving St. Vincent’s administration, which was carried without a division, Jeffery’s fiasco was complete. Canning was horrified that ‘this stupid, pigheaded, obstinate Jeffery’ had spoilt such a good question.
Jeffery was not entirely silenced by his débâcle. On 23 May 1806 he suggested, in the debate on the American intercourse bill, that Newfoundland could supply the West Indian colonies with five times the fish they required. He survived ministerial hostility at the election of 1806 as no opponent materialized: such was his story to the House, 13 Feb. 1807. He was listed a staunch friend to the abolition of the slave trade. On 21 Mar. 1807 he hoped for office under the Portland ministry, writing to George Rose:
I trust that my past conduct in Parliament will justify my writing to you in the present situation of public affairs. Having relinquished all commercial concerns I am quite at liberty and do not scruple to say I am anxious to have some share in public business if the nature of the arrangement now on the tapis will admit of it. Having gone thus far in anticipating my wishes to you, I trust I shall stand excused in pointing out the Admiralty, Treasury or Ordnance as situations most congenial to my inclinations.
Nothing was then done for him. He was a ministerial sniper during the debate on Brand’s motion, 9 Apr. 1807. Although he headed the poll at Poole in 1807, his competitors tied for second place and one of them petitioned the House, throwing in the allegation that Jeffery lacked the property qualification and was additionally disqualified by an Admiralty contract. He retaliated by drawing the House’s attention to the vexatious delay in delivering the Poole writ, 16 July. He was left secure in his seat, but his only game now was waiting for a place, of which he was doubtless in financial need. On 5 Oct. 1808 Huskisson informed Spencer Perceval:
Jeffery has long been looking for a seat at the victualling board, and ... he will be out of all humour if some other promise is not made for him, before a new arrangement takes place—I do not think him a fit person for a seat at the board.
Instead he was offered the consulate at Lisbon with a guarantee of the first £1,500 of consular fees and a quarter of the surplus. He vacated his seat, though there was some debate as to whether it was necessary, there being no exact precedent.