OP, I also don't have a particularly pronounced Norther accent.
I used to work in our Birmingham office.
A colleague I was speaking to on the phone at our Gulidford office once said to me, entirely in earnest "why don't you come and and work down here, you sound as if you come from somewhere proper originally anyway?"
I also very recently had a colleague who lives in Kent say quite unashamedly "yeah I fort Swindon was some shithole ap norf till I went there and it's actually quite OK"
Victoria Wood mentioned this - she said no-one in the Media understood why she didn't live in London (until she did) - I think that was the source of the Continuity Announcer gag that a pp posted.
I'm quite often told about the superior culture, diversity etc in the South by people who will happily confide they never venture North of Watford.
I don't like it, by the way, I think it's corrosive and unhelpful.