Middleton’s family, who had been settled at Belsay in Northumberland since the thirteenth century, had represented the county since early in the fifteenth. After the Restoration they were one of the few big landowning families to remain Presbyterians. During Middleton’s minority his chief trustee was the Presbyterian minister at Belsay and his mainstay at elections was the Presbyterian vote, which was especially strong among the farmers.1‘Account of Fam. of Middleton of Belsay’ by Sir Arthur Middleton, 7th Bt., in possession of Sir Stephen Middleton, 9th Bt. In spite of this he became a member of the Jockey Club and the owner of a first-rate stud, bred from newly imported Arabians.
On coming of age Middleton was returned as a Whig for the county, which he continued to represent for the rest of his life. He usually supported the Government but voted against them on the excise bill in 1733 and the place bill of 1740. In May 1742 he was one of the members on the court list who were chosen as commissioners of public accounts under an opposition bill which was thrown out in the Lords.2Walpole to Mann, 26 May 1742. When the Duke of Cumberland passed through Northumberland in January 1746 to assume command of the army in Scotland, he took Middleton with him, ‘making him, though a civilian, a colonel and placing him on his staff’.
According to family tradition Middleton ‘was always borrowing money and always in debt’,3‘Account of Fam. of Middleton.’ probably owing to the enormous cost of the county election of 1734, which also crippled Ralph Jenison. From 1754 he appears in Newcastle’s secret service accounts as receiving a pension of £800 p.a., but when it started is not known.4Namier, Structure, 217-18. He died 28 Sept. 1757.