I'm looking at getting a used estate for around £15-18k budget. I'll need it three days a week to go between Bristol and Cardiff and would drive through/around Cardiff City Centre.

I'll also do some long business trips as well, and holiday trips so likely around 8-10,000 miles per year. I've never owned a diesel and, of course, wary of any charges they may introduce for these cities, as well as running/maintenance costs. Which cars would you suggest?