I can handle maybe 99% of what they are saying. Watching Brit TV since a young kid helps I guess.
Life On Mars and Ashes To Ashes required some subtext a few times with Gene, Chris and Ray.
And I leave the subtitles on for “House”. Not only does it help to understand what’s going on sometimes, but as an added bonus, it identifies the music by title and artist, which normally I wouldn’t care about, but I discovered that the musical selection is often chosen based on theme (ie, the title of the song fits in whatever just happened).