I was a student in Bangor in the 80s, the locals had an odd accent, closer to a Cardiff accent than standard North Walian, with a bit of scouse mixed in, within a mile or so across the Menai Straight it was the full on Gog accent. I did a teaching practice in a school in Holywell where the accent was differrent again, a very nasal sort of North Walian/ Manchester. One kid sounded full on scouse, when I asked why I was told he’d moved from Connah’s Quay where they all spoke like that, it’s only 2 or 3 miles down the road. I guess it very localised all over.