I grew up in the South East, in and around Royal Tunbridge Wells. I went to university up north and uni friends, housemates and course-mates (vast majority Northerners) would often remark on the way I pronounced things, particularly the classics like ‘grass’ and ‘bath’. One person would repeat the word/phrase in an over-done RP accent and the rest of the group (including me, most of the time) would get a bit of a giggle out of it. People would often assume I had loads of money and my family were landed gentry or Viscounts or something.
I went to the ‘second’ university in the town (an ex-polytechnic) and, interestingly, people I met who didn’t know that, would assume that I went to the ‘primary’ university in the town, renowned for being (better) and with higher entry requirements.
Definitely found myself inadvertently adopting a bit of a Northern twang by the time I got to third year!