This is superb drama - rare for the BBC but then this was 2008,. Now the only decent drama on BBC is bought in from private production companies (Vienna Blood, Peaky Blinders, The Night Manager etc). Most is lazy easy drama for the largely female middle-aged audience (Call the Midwife anyone?)
This would have been 5 stars BUT it sags badly at the end. That last episode (no spoilers) was maybe not necessary, if the penultimate episode were tweaked. THAT is precisely what they did in the US remake THE NIGHT OF (2016), also good with a snappier ending. They cut the flab and it works better.
However, the first 4 episodes are brilliant. Ben Wishaw is brilliant in everything he does and other actors do well too. The late Pete Postlethwaite is superb in one of his last performances; not sure about David Harewood who always seems to play...David Harewood. Michael K Williams in the US version was so much better. Nice to see Southend again as well.
I would say the plot is not realistic. Again maybe the US version is more believable. But hey, it's drama! It can do that if written well, as this is.
Watching series 2 soon but do not expect it to be as good as series 1.
Anyway 4 stars. Decent British crime drama, for once.