Outside of Britain proper, but in what was then a British dependency, you had the United Irishmen revolt at the end of the eighteenth century, in which (as the

Outside of Britain proper, but in what was then a British dependency, you had the United Irishmen revolt at the end of the eighteenth century, in which (as the name might suggest) Protestants and Catholics made common cause. That must have caused some alarm in London. It did inspire similar movements in Britain itself -- United Englishmen, United Scotsmen, United Britons -- but they don't seem to have amounted to much.