In 1727 Leathes, on succeeding to his uncle’s fortune, which included an estate near Harwich, ‘made interest ... to be chose’ there, but in the end was returned for Sudbury. ‘A man of ... good parts’, with ‘a very plausible way of telling his story’, he was described in 1733 as ‘a friend to the Government, a sure one, and has not given a vote against us’.
In 1733, learning that the sitting Members for Harwich, Lord Egmont and Sir Philip Parker, intended to retire at the forthcoming general election, Leathes applied to Walpole for the government interest there. After consulting Egmont and Parker, who raised no objection, Walpole agreed that the government interest should go to Leathes and Egmont’s son, Lord Perceval, standing jointly, i.e. on the understanding that each should do his best to secure that his supporters gave their second votes to the other. But at the last moment Leathes, declaring himself unable to persuade his supporters to carry out this compact, joined with a third candidate, Charles Stanhope, against Perceval, who was defeated, leaving Leathes in control of the borough.
In 1741 Leathes nominated his brother, Hill Mussenden, to succeed him at Harwich, reverting himself to Sudbury. He supported the Administration till the end of 1743, when he and his brother voted with the Opposition on a motion to discontinue the service of the Hanoverians from British pay,
He has for many years been trying to take this borough from the Crown, and once had it, viz. from year 1734 to year 1742. He will not have it again if I live.
Namier, Structure, 368, 379.
He died in 1780.