Smallpiper: I see it as the key event that reversed the political expansion of the English (taking the Northumbrians as one of the leading political elements of the English). England as a single state did not exist at that time, true, but English as an identifiable people, with a common language, heritage and similar political organisation, did. It was the loss of Fortrenn and the collapse of Northumbrian control of the Scottish Lowlands that established the current borders, and nationalities (give or take a few miles here-and-there and over a thousand years).

McGrath: I half agree, with qualifications as to the geographical extent. Had the battle gone the other way, perhaps we could have had a Northern England from Lincoln and Cheshire up to the Grampians, including Clydeside. Whether this would have survived as an independent state against the combination of Wessex and Mercia or not is debatable. And later the Danes, the Vikings, etc etc...

I am still drawn by the statement that the term Sassenach was initially applied by the Gaelic-speaking highlanders to the Lowland Scots, who are thus clearly within the English/Anglo-Saxon world.