Onslow, son of Speaker Onslow, was embroiled in the controversy over John Wilkes, and moved that his re-election for Middlesex in 1769 be declared invalid. He was present at the secret marriage of the Prince of Wales to Mrs Fitzherbert in 1785.Dyson was nicknamed 'Mungo' (the ubiquitous negro slave in Isaac Bickerstaffe's 'Padlock') from his omnipresence in parliamentary business (DNB). He discontinued the practice of selling the subordinate clerkships in his office. He was a friend of the novelist Richardson and settled a pension on Mark Akenside, the poet and physician.