The story about the conversation between people from Yorkshire and Denmark arose when some Danish soldiers were billeted in East Yorkshire (I think during the First World War). The E Yorks dialect is (was) very different to that of other parts of Yorkshire. My grandfather was able to speak it (though he rarely did), having been born and bred on the Wolds. This dialect is said to go no further east than Selby (presumably because it couldn't swin across the river).

I've jst found this piece:

"It has to be said, though, that for most Yorkshire speakers, this isophone has now drifted northwards to the Tees. Even so, a number older speakers (particularly in the remoter parts of the Dales, the North York Moors and the Yorkshire Wolds, do still preserve some of these Old Northern vowels. One hundred years ago, however, the change would have been instantly noticeable the moment you "crossed the line". The distinction was particularly sharp at Selby, where the isophone followed the line of the River Ouse, dividing the West and East Ridings. Today, you really have to visit Durham and Northumberland to be sure of hearing younger speakers using the old northeastern forms."