Part slasher movie, part murder mystery – has Line of Duty gone a bit too far?

Where are French and Saunders when you need them? Surely no TV drama in recent years has been so ripe for a spoof than Line of Duty – perhaps Dawn and Jennifer as Steve Arnott and Kate Fleming, exchanging covert glances and conversing entirely in acronyms. Or Jen as Ted, spewing forth the gaffer’s legendary colloquialisms (“Mother of God! I don’t float up the Lagan on a bubble”, and so forth). I mean all this as a compliment, of course, because you don’t get parodied until you’re an institution, which is what Line of Duty seems to have become over the last six weeks.

But has it gone a bit, well, OTT in this latest series? Sunday’s feature-length finale summed up for me the series’ strengths and weaknesses – the main strength being the super-extended interview scenes between Anna Maxwell Martin’s Carmichael, all fake smiles, and Adrian Dunbar’s increasingly forlorn Ted Hastings. I timed these head-to-heads: they lasted 45 minutes – quite extraordinary for a modern-day TV drama.

This intense and intimate hyper-realism sits somewhat awkwardly beside what happened next – part slasher movie (rogue WPC Tina attacking the unmasked Gill with a knife in the women’s toilets; all we lacked was Bernard Herrmann’s Psycho score) and part Agatha Christie whodunnit, as Steve finally twigged what the dying “Dot” Cottan (Craig Parkinson) was doing with his fingers. Yes, Dot’s digits were telling us that there was a fourth corrupt police officer still at large – and therefore a sixth series of Line of Duty. I hope actor Parkinson is receiving residuals.

So, we still don’t know the identity of “H” – it has become a national guessing game now. Going into the final episode, plenty of viewers were wagering that legal counsel Gill Biggeloe (Polly Walker) was a bad’un – if not the ultimate bad’un – so that didn’t come as much of a surprise. It was surely never going to be Ted, who might as well have been walking around with a sign on his head reading “red herring”.

Anyway, after five series, certain LoD tropes have established themselves. That Stephen Graham’s rogue undercover cop was knocked off at the end of episode four, for example, wasn't a massive shock, given that writer Jed Mercurio has form in dispatching his high-profile guest stars at unexpected moments (and not just in Line of Duty – see Keeley Hawes in Bodyguard for further details).

The raid on the police convoy in episode one seemed unoriginal, echoing the convoy ambush in series two, while the need to tie up loose ends wasn’t always satisfactory: Ted disposing of his laptop because he’d been watching porn (and nothing illegal at that), for example, or the AC-12 office becoming a haven for body snatchers.

I quite like that Line of Duty is not set anywhere in particular, but that does add to the sense of dislocation, of a world not quite connected to our world. One where, for example, the Home Secretary wouldn’t become embroiled in a £50m theft from a police depot or the murder of three policemen, and the media appear virtually non-existent, while the rare incursions into the main characters’ private lives seem cursory. Ted’s time in Northern Ireland became pivotal, but the fact that Kate was never home to tuck the kids into bed... do we care?

Don’t get me wrong, Line of Duty remains a thrilling white-knuckle ride, but I don't think that the show – although intelligent – is as profound or relevant as the work of Mercurio’s predecessors. GF Newman’s Law and Order, for example, or Troy Kennedy Martin’s Edge of Darkness. Nor is it as good as the drama it most resembles, JC Wilsher’s 1990s police corruption saga Between the Lines (incidentally made by the same production company as Line of Duty).

Still, this is peerlessly visceral entertainment, and where the writer goes with series six, I’m still agog to find out. It’s bound to be ingenious and somewhat implausible. And we’ll still have Ted, Steve and Kate. That is, until we don’t. As Adrian Dunbar told me, “the first thing you do with the script is check you’re not dead”.