Another account attributed the failure of his remonstrance against French aggression in Corsica to the indiscretion of Lord Mansfield, who at the table of a minister in Paris was said to have declared that the English cabinet was too weak and the nation too wise to enter upon a war for the sake of Corsica (Stanhope, v. 199; cf. Walpole, Mems. of George III, ed. Barker, iii. 154). In retribution Rochford plied the ministers with alarming tales of deep-laid designs for a French coup de main upon Gibraltar. On 21 Oct. 1768 Rochford was appointed secretary of state for the northern department in place of Lord Weymouth, who replaced Shelburne in the southern; Shelburne withdrew from the administration upon the retirement of Chatham. Rochford owed his nomination to the new prime minister, the Duke of Grafton. The new secretary vindicated his independence, if not his judgment, upon a momentous occasion. On 1 May 1769 at a cabinet meeting Grafton proposed to his colleagues that they should altogether repeal the obnoxious American duties. To avoid an appearance of timidity, North urged that the tea-duties should be excepted from the repeal. On a division the proposal of Grafton was rejected by the casting vote of one—Lord Rochford. But for this unhappy event, wrote Grafton afterwards, ‘I still think that the separation from America might have been avoided.’ In December 1770 Rochford, though still nominally under Weymouth's direction, showed his accustomed skill in dealing with the politicians of Madrid, Spain conceding everything that England asked, though not until the English minister had left the Spanish capital and had proceeded twenty leagues on his homeward journey. The committal of Spanish interests to the care of Rochford, who still retained the northern department, was apparently a concession to the criticism of Junius, who had written (Letter i. 21 Jan. 1769; cf. Letter xlix.): ‘Lord Rochford was acquainted with the affairs and temper of the southern courts—Lord Weymouth was equally qualified for either department. By what unaccountable caprice has it happened that the latter, who pretends to no experience whatsoever, is removed to the most important of the two departments, and the former by preference placed in an office where his experience can be of no use to him?’ [see Thynne, Thomas, third Viscount Weymouth and first Marquis of Bath]. Fear of giving offence to Choiseul was openly stated in the commons to have been the ministerial motive in excluding Rochford from any share in our diplomatic relations with the Bourbons (Cavendish, Debates, 1843, ii. 184). He was, however, moved to the southern department on 19 Dec. 1770, the promotion being effected by means of an exchange with Weymouth, who did not ‘choose to be dipped in the Spanish business’ (ib. iv. 171). Numerous references to his activity as secretary, especially in reference to Irish affairs, are contained in the second volume of the ‘Dartmouth Papers.’ In connection with the ‘Convention with Spain’ of 1771, the ‘London Museum’ presented its readers with a portrait of Rochford, engraved by J. Lodge, with the legend from Gay, ‘Man may escape from Rope and Gun, but Infamy he ne'er can shun’ (April 1771).
In October 1775, in view of the American difficulties, Grafton and Rochford resigned. The latter was spoken of next year as lord-lieutenant of Ireland, but eventually received, as a consolation for the loss of his secretaryship, a pension of 2,500l. a year (Letters of George III to Lord North, i. 286–92); this was almost immediately increased, and on 11 Jan. 1776 a grant passed the great seal for an annuity of 3,320l. payable quarterly (Gent. Mag. 1776, p. 44). A good deal of annoyance was caused to the government at the time of his retirement by his maladroitness in drawing up a warrant for the arrest of Stephen Sayer or Sayre, a banker in the Oxford Road, London, who published a pamphlet in remonstrance and in vindication of the liberty of the subject. Sayre eventually brought an action against the secretary before the court of common pleas on 27 June 1776, and Rochford was cast in damages to the amount of 1,000l. (Report of Trial, 1776, fol.). The incident, however, was soon forgotten; Rochford was made master of the Trinity House, and in 1776 paid a visit to his estates in Holland. In April 1778 he made some overtures to Chatham, which came to nothing (Stanhope). He was elected a K.G. on 3 June 1778. He died at St. Osyth priory on 28 Sept. 1781, aged 64, and was buried at St. Osyth, the property which had come to him from his mother's family (see Wright, Essex, ii. 775).
Rochford married, in May 1740, Lucy, daughter of Edward Young of Durnford, Wiltshire, sometime Bath king-of-arms. She had been maid of honour to Queen Caroline when Princess of Wales, and she died without issue on 9 Jan. 1773, aged 50, and was buried at St. Osyth (Lloyd's Evening Post, 1 Oct. 1781). Rochford at his death had to dispose of a landed property of 2,000l. a year, which by his will he gave as follows: ‘To Mrs. Johnstone, a woman who lived with
