Why would anyone suppose there would be a uniquely "English" instrument, as opposed to a Scottish or Irish or Welsh one? Those national borders were laid down by bunches of Normans fighting each other basically.(Wallaces, Bruces and Stewarts north of the border v Planataganets south, for example). Musicians happily got on with music, irrespective of who briefly occupied the Big House.A Roman Wall can occasionally stop a large army of Picts and Scots. But it will always be porous to an itinerant harper who pootles into the fort from one side, earns a couple of denarii singing in the canteen in the evening, and departs the following morning on the other side. Having left a little music, and picked up a litle more.