Is the question really where to find them or are you looking for recommendations? As far as where you can find them, you can look for shows to purchase or rent at iTunes and Amazon, and of course there are many not so legal ways of downloading them. I also believe many of them are posted on YouTube (they get uploaded and are often eventually removed). The advantage of legal downloads is that you can watch with subtitles, which makes it much better for learning English. But even in the case of illegal downloads, there are many sites where you can find the subtitles separately. As far as what to watch, I am not familiar with the current British shows. The shows that I've seen over the years that have that classic clean and proper British are mainly the literary adaptations such as Miss Marple, Hercule Poirot and Sherlock Holmes series. Just make sure you get the BBC versions as there are US editions of some of them. "Downtown Abbey" and "Inspector Lewis" come to mind as well. There are also tons of great comedies such as "Fawlty Towers" and "Blackadder", those probably have a good proper language balance. Shows like "Allo Allo" and "Only Fools and Horses" are amazing but leave them for the second stage of learning, after you are ready to move away from proper British.