I agree with you, Brian, that it makes no more sense to talk of Scottish, Welsh or Irish (or indeed of any other ) 'races' than of an English one. ( I wondered however whether you are right to call the Irish 'basically Britons'. I suppose many of them may have arrived in Ireland from Europe via Britain in prehistoric times, but does that make them 'Britons'?)

I suppose there was an 'English Empire' - perhaps several separate empires - before England and Scotland joined to become 'Great Britain' in 1707. As well as Ireland (our first overseas possession?) and Wales, it comprised, at one time, parts of France and, later, the North American colonies and various possessions in India and the Caribbean.

As you say, Scots played a major role in the British Empire of the eighteenth century and later. Indeed, some historians claim that it was the Empire more than anything else which created the 'British' national identity. That is one reason why, as an anti-imperialist, I feel uncomfortable with the notion of 'Britishness' and would rather think of myself as English. (I really hate being called a 'Brit', and sometimes fantasize about the word eventually becoming as politically incorrect as 'Paki' and 'Chinaman.')