I'm working on a series of stories set in the UK right now. I'm not British but I have a lot of people reading these stories who are. I find that I'm constantly on alert when I write dialog because I don't want the cadence and vocabulary to be incorrect for the dialect. It's tough but sometimes I'm also using it to my advantage to make the conversations which should be stilted and uncomfortable even more so because I as the writer am stilted and uncomfortable within them.