In April 1814 Vice-Admiral Sir Alexander Cochrane made the British position official: All those who may be disposed to emigrate from the United States, will, with their Families, be received on board of His Majesty's Ships…. They will have their choice of either entering into His Majesty's Forces, or of being sent as FREE Settlers to British possessions, … where they will meet with all due encouragement. Cochrane then ordered Rear-Admiral George Cockburn to form the Colonial Marines, fighting units made up of refugee slaves.
All told, more than 4000 people were freed from slavery – the largest emancipation that took place in the U.S. until the Civil War.
http://www.pbs.org/wned/war-of-1812/essays/black-soldier-and-sailors-war/