If you were to go back 500 years or so, I don't think there would be much to distinguish the origin of most British Isles (or Northern Eurpoean) music apart from the language of the lyrics. Certain instruments give regional clues, too, although thses would occur later on.

Since then, the English set about empire building and much value was placed on having travelled and seen the world, so a lot of foreign music and cultural references were added to the popular canon. Meanwhile, the Irish and the Scots continued to be persecuted by the English and invested much more of their national identity into their music, which has, as a consequence, remained much less altered over the intervening period. The vestiges of English music remained mostly in martial music and, as John Kirkpatrick says, you can recognise English tunes because you can march to them.

The modern Celtic sound is a generalisation based on instrumentation and ornamentation style which needs care if you then refer to all the tunes as Celtic. There are a number of tunes of English origin recorded by Celtic groups which have been "Celticised" and you wouldn't know their true origin. Those would be the ones with balls and oomph, Red.

English traditional music has been withering on the vine since we stopped valuing our cultural heritage as a nation. When you compare Morris with the vapid and uninteresting circle dances which are revered in many European countries as their traditions, we should be proud to have something with some vigour and violence in our culture, apart of course from football hooliganism.

I suppose the English left their country to conquer and bring back other cultures, the Scots and Irish left to escape poverty and took their culture with them. Certainly, the Irish tradition is far stronger abroad than in its home country, where Nashville holds sway almost everywhere.