I know I probably just ruined a lot of your childhood images of Paul Revere on his brave steed proudly waving the American flag as he warns his fellow patriots, "The British are coming!"
The real truth is at the time of Paul Revere's famed 'Midnight Ride', American Colonists still considered themselves British. Had Paul Revere really told people, "the British are coming," it would have been like saying, "we're coming." Doesn't make much sense, does it?
It's more likely Revere would have said, "The Redcoats are coming" or (according to witness reports at the time) "
The Regulars are coming out" to signify the difference between the British from England and the British from the American Colonies.
I'm not really sure when the phrase, "The British are coming," became associated with Paul Revere. It's likely that it's a phrase that became popularly used during the War of 1812 at which time the United States, now populated by people who firmly thought of themselves as American, declared war against the British Empire.