What assumptions do you make when you hear the accents above? Where do these assumptions come from?
Think about where you might hear the accent(s) in film/TV/entertainment and what you associate these accents with.
I associate the Cockney accent with policemen, because of TV shows set in London (like Sherlock). I would associate a Cornish or west country accent with farmers because there are a lot of farms and countryside in that area, so on TV farmers tend to be given that kind of accent.
Why do you think that different British accents have certain assumptions made about them?
The only time a lot of people hear different accents is through television, where actors are playing different types of characters. This creates assumptions that people who live in that area are similar to the ones they have seen on TV. I think that on TV people with regional accents are a bit rough and less rich than someone with a standard or posher accent. Abroad, British accents tend to be associated with being very posh, probably because of their knowledge of the monarchy, and because of older TV shows where people used to speak in RP.