What I think is:- the reason Wogan refers to the UK entry as 'us' because he's being paid to do the commentary by the British Broadcasting Corporation. Britain is 'us' as far as the BBC is concerned, and that's who he's representing.
I didn't see the ESC, but I've seen the Scooch thing. Woefully embarrassing, I thought it was. They ended the song by displaying a couple of Union Flags - I can't believe that anyone would think that triumphantly displaying your own country's flag is a good way to get people from other countries to vote for you, but there you are.