Err....my history is a bit shakey, but surely 'the English' in the ancient battles you mention includes lowland Scots?
I was born in England and moved up to Scotland to go to Uni and stayed here ever since - 44 years except for a couple of years in Yorkshire and another couple in Anglesey. I married a Scot (who is often thought to be English because he doesn't have a broad accent) and have one son born in Scotland, the other in England, both 'genetically' half and half

. The Scots born one had some major racist issues when he worked in England - such as 'f### off back to your own country you f###### Jock' Great - it's not just one sided and at the moment I often feel that the anti Scots climate in England is fuelled by the Government knocking the Scots over devolution and independence ie it suits their political ends. So between Braveheart on the one hand and some stirring from the Westminster folk (even the anti independence Scots) via the media, racial antipathy has become mutual, although based on prejudice not knowledge. Huge shame and what a load of claptrap. I love having all sorts of people from other nations here, even when there are major problems as new families settle into Britain.
But shygirl's experience was the other way round. I think a lot of how you feel about this, and whether or not it persists, is about how you react to it. As with every bullying situation, if those doing it feel they have scored a hit then they will persevere. If you turn it into a discussion not a row then that will help to defuse the situation. Jumping on high horses, however offended you actually feel, will not help in any way, but may well just fuel the negativity. I think it's true that once we get to know individuals of whatever nation, then we stop 'hating' (ie prejudging) the whole nation.
There is and I think always has been, this tendency amongst humans to notice the differences between their group, be it clan, nation, accent, language, beliefs or financial status, and to fight about it. Look back through world history and that's about all you see. Lack of racial prejudice is a sign of good education and of increasing globalisation. I can quite imagine that once as a world we meet another inhabited planet it will revert back to 'us' and 'them', where the 'us' will be all the nations of Earth.