Having previously served as a seat-warmer for George Forester, Simpson was again returned for Wenlock when his father was raised to the peerage. In his first Parliament he had followed his father in opposing Pitt. He joined the Whig Club, 3 Apr. 1786, and Brooks’s Club, 15 Dec. 1792. On his return to Westminster he was expected to support Pitt’s administration with the Portland Whigs: but he was negligent. He was never opposed at Wenlock, but his was the more vulnerable of the two seats and his return depended on the regular endorsement of the independent interest there. Temperament and circumstance thus combined to make him an unpredictable independent, though his obituary classed him one ‘of the old Whig school’.
Simpson appears to have voted with opposition for Grey’s amendment to the address, 2 Feb. 1801, unless it was his namesake, the Member for Mitchell. He was listed a supporter of Pitt’s second administration, but voted for the censure of Melville, 8 Apr. 1805. He was expected to support the Portland administration. In March 1810 the Whigs listed him ‘hopeful’, but he did not raise their hopes until late that year when he was described as having deserted government on the adjournment, 29 Nov.
Simpson was not on the list of Treasury supporters after the election of 1812. There is little evidence of his attendance during that Parliament. He paired with opposition for inquiry into the Regent’s expenditure, 31 May 1815. A year later he contemplated retiring in favour of his nephew Lord Newport when a dissolution was rumoured. He did not do so, but in the next Parliament only one vote is known, in favour of Tierney’s censure motion, 18 May 1819. After this bold gesture, Simpson retired in 1820, though his nephew declined to offer as his successor. He died 5 June 1850, best known as an agricultural improver in Nottinghamshire.