'Let us therefore brace ourselves to our duties, and so bear ourselves, that if the British Empire and its Commonwealth last for a thousand years, men will still say, "This was their finest hour".'
Your task is to make this a reality - have the British Empire last for one thousand years or more (assuming 1707 to be the starting point).
Bonus points if you can do this without having the Empire morph into a Commonwealth or Imperial Federation.
I've put in this in pre-1900 to allow for maximum flexibility.