 A strong supporter of King Charles I in the English Civil War, which broke out in August 1642, Grandison spent his fortune on horses and equipment for a regiment of Cavaliers in support of the king.On 23 October 1642, Grandison's regiment was on the royalists' left wing at the Battle of Edgehill.During the fighting, the king's standard-bearer, Sir Edmund Verney, was killed, and the royal standard captured.