In the years before the Pitkin Affair broke, Brerewood served as an agent to some of the leading army commanders of the day. He was the paymaster for the Duke of Marlborough’s battalion in England while Marlborough was the commander-in-chief of the English army fighting in the Netherlands against the French during the War of the Spanish Succession (1701-1712). He also acted as agent for the regiments of the Duke of Schombergh; of Colonel Cadogen, the commander of a cavalry company; of Lieutenant-Colonel John Bristow of the First Foot Guards; and of the Duke of Northumberland, who would become Brerewood’s particular patron.