George Munro having returned to Scotland with 1200 horse and 2100 foot soldiers was sent to support the royalist James Hamilton, 1st Duke of Hamilton. The Scottish royalists were defeated at the Battle of Preston (1648) by the Parliamentarian forces of Oliver Cromwell. But before the battle Munro had refused to serve under James Livingston, 1st Earl of Callendar who was the second in command under the Duke of Hamilton. An argument had ensued, and as a result Munro's involvement in the battle was limited. George Munro had an intense dislike for Callender, and Callendar saw no reason why Munro should be allowed an independent command.