While I amsure the British would have paid no attention to the rwo bits of wartime opportunism you cite, slavery would have ended here in the 1830’s if the American Revolution had failed. It is called the irony of history, Henry Kissinger is particularly fond of the phrase which means sort of a cosmic horselaugh at human asperations to control the course of events.
In fact the British didn’t ignore those emancipation proclamations and blacks who benefited from them ended up in Canada, free.
I suspect that history gets ignored here in the States since it tends to take the shine off of some of our own national mythology.