Just from the viewpoint of geographical boundaries, maybe there's enough commonality (in overlapping bands of musical interest) from the south east of Scotland down to the Tees to justify the broad definition of Northumbrian music, but, let's face it, it's murderous to pin down. Just think where you might draw the line round Irish music - just what comes from the island itself, just from Eire, how about including the diaspora? - and I guess it's a universal problem. Music is pretty darn portable!

But most people seem to agree that Northumbrian tunes are tricky. Possibly down to input into the tradition from particular virtuoso players/tunesmiths like James Hill the fiddler and Tom Clough the piper? And, of course, those temperamental pipe chanters.