Brigstocke was related to Lewis Pryse, the leader of the Cardiganshire Tories, who recommended him as his successor.
A year or two before his death, 4 May 1746, he wrote to Walpole, now Lord Orford, asking for the promotion of a nephew to a lieutenancy in an old regiment. The letter concludes:
The honour I have had of being an old school fellow of your Lordship’s about fifty years ago, with the frequent civilities you have shown me since, and above all your humanity and good nature, have brought this trouble upon you and will I hope be a means of procuring your pardon for it.
11 May [?1744], Cholmondeley (Houghton) mss.