I hadn't watched seasons 1 and 2, so I started on Season 3. I have two episodes to go. I am riveted. Anna Friel is so good. It took me to episode six to get the story straight. I'll definitely go back and watch series one and two after I finish.
I'm currently on Season 2, having just finished Season 1 .. and have to say that it was only at the last episode that I figured out the who-dunnit!!! Loving the fact that many of the scenes are shot in East London where I was working when living/working in London! Ah, the memories ..