Spent six months in Portsmouth, many years ago, when on a course with my job, and I've got to say I found their accent to be very country sounding, and still do. It certainly isn't plastic cockney, unlike where I currently live in Kent.
Then again I have a fairly neutral southern accent, and often hear (particularly older) people from rural Oxfordshire and think they sound as if they've just got off of a combine harvester!
I do think the Oxfordshire accent has changed over the years and become more southern/estuary, particularly in the young and the further east you go in the county.