On arriving in London Barret was able to build on the contacts that he had made in Ireland and particularly with the political faction that had grown up around Marquess of Rockingham known as the "Rockinghamites" or Rockingham Whigs. Rockingham was to become prime minister in 1765–1766 and again in 1782. The connection was through Edmund Burke, Rockingham's private secretary and prominent Rockinghamites who commissioned paintings from Barrett were the Duke of Portland, the Earl of Albemarle and Sir George Colebrook. His patrons were mainly the rich landowner who wished to have their estates and parks recorded. Barret soon found himself with numerous commissions and it was rumoured that he was earning up £2000 a year, a princely sum for an artist at the time. Contemporary accounts suggest that Barret was a highly sociable character and got on well with people and other artists. Even though Richard Wilson made disparaging remarks about both Barret and Gainsborough at the same time, Bodkin maintains that Wilson and Barret were personal friends. It is noticeable that many of the landowners who patronised Barret were in the process of building impressive new mansions which would require large oil paintings to decorate the reception rooms. The Duke of Portland at Welbeck Abbey, Sir Peter Leicester at Tabley and the Marquess of Rockingham were all employing Carr of York as an architect and this may provide a link between his early commissions after Barret arrived from Ireland.