IT IS commonly acknowledged among film critics that there are two truly great trilogies.

The Godfather, obviously. And the all-time number one, Toy Story. Now, though, at the end of three extraordinary series, they have a small-screen cousin.

Take a bow, BBC2, writer Jed Mercurio and everyone involved in Line of Duty.

It’s not just the best British TV drama of the year (up against stiff competition already), it’s the best TV show of the decade.

If you haven’t watched last night’s thrilling climax, or indeed any episode, first off, what the heck have you been doing since 2012?

But secondly, I’m not holding back from spoilers here, so please, stop reading, do yourself a favour and catch up pronto with the investigations of Supt Ted Hastings’s anti-corruption unit AC-12. Because, to my surprise and great joy, last night’s unflinching finale wrapped up the loose ends perfectly, with the bad guys getting the comeuppance required after an unsatisfying climax to the previous, otherwise outstanding, run.

The mob’s inside man, corrupt DI Matthew “Dot” Cottan, aka The Caddy, is dead.

He’s one of the great TV villains, played with superb shifty menace by Craig Parkinson.

By the end you almost felt sorry for him as he took a bullet to save DC Kate Fleming, the colleague who brought him down, and use his last breath to nail VIP paedophile ring cover-up monster Chief Supt Patrick Fairbank.

It was a dramatic, high-octane last 10 minutes. But where Line of Duty sets itself apart is the police interrogation scenes and the finale was anchored by two – of Cottan and DS Steve Arnott (the magnificent Martin Compston) – lasting half of the 90 minutes.

Nothing’s hurried in that interview room. Your typical preamble to a question begins with: “On screen you will see image 291 and 292 showing item references MR3 and MR4.”

The trick it has mastered is to ratchet up the tension almost so it’s unbearable by mounting the evidence slowly, but irreversibly, against the suspect.

It has a wonderful script, exceptional acting, unforeseeable twists such as the murder of a seemingly major character in series’ openers and doesn’t flinch when it comes to killing off its stars (RIP DI Lindsay Denton, Keeley Hawes’s finest work).

Mercurio doesn’t shy away from sailing close to the wind either – a photoshopped snap of Jimmy Savile with Line of Duty abusers is nothing if not daring.

The timing of the Hillsborough inquest verdicts has also brought police deception into sharp focus this week.

Viewers with good memories will remember gangster Tommy Hunter in series two threatened to inform on corrupt officers “from the two-faced b****** right down to The Caddy”, suggesting some uniformed bigwig is the real criminal mastermind. Cottan naming Fairbank as the kingpin issuing his orders looks like solving that mystery.

But this is Line of Duty. And series four is in the pipeline. A fact you’d assume I’d welcome.

There is, however, this nagging concern they should have ended it here, at its zenith, with all plots complete, retiring like Neil Morrissey’s crooked DC Nigel Morton, on full pension and fraudulent disability benefits.

I hope I’m wrong, but it feels like Duty’s done.

Spudulikes…

Louis Theroux: Drinking to Oblivion.

Caravanner of the Year’s disarming charm.

Ronan Keating’s A-list mobile phone contacts making the Send To All game on Michael McIntyre’s Big Show the comedian’s greatest moment.

David Walliams’ BGT golden buzzer act Ian and Anne Marshall “picking a Beyonce song for no apparent reason”.

The One Show booking Captain America: Civil War stars Paul Bettany and Anthony Mackie to play Jenga.

And sexy dancers Forbidden Angels on Britain's Got More Talent, with Anthony McPartlin’s reaction as they writhed under a shower: “Oh yeah! Yeah-yeah-yeah-yeah, yeah! Yeah-yeah-yeah-yeah-yeah-yeah, YEAH!” But did Ant and Dec press the golden buzzer when it was needed? Oh no! No-no-no-no, no! No-no-no-no-no-no, NO!

Spuduhates…

C4’s morose Flowers (save them for a funeral).

An extra hour of EastEnders turning likeable Jay into a paedophile.

BBC1 London Marathon reporter Colin Jackson’s contradiction in terms: “I’m with two very famous faces from Hollyoaks.”

TLC’s Vogue (Williams) Does The Afterlife giving airtime to the bogus art of psychic mediums, featuring one subsequently jailed for theft, which wasn’t mentioned.

And Esther Rantzen on her The One Show vox pop about a 17-year-old daughter wanting her boyfriend to stay over in her bedroom: “Parents are much more lenient with sons than with daughters, so if you want to get up to anything, go to his place.” Probably not the founder of Childline’s wisest ever words.