Line of Duty: Jed Mercurio reveals clue to identity of ‘H’ was hidden back in season one

Identity of the villainous ‘fourth man’ was revealed during the sixth series finale

Line of Duty creator Jed Mercurio has revealed that a clue was left foreshadowing the identity of “H” way back in series one.

The mystery of “the fourth man”, formerly known as “H” (the name given to a criminal mole working within the upper echelons of the police), was finally resolved during the sixth season finale which aired last Sunday (2 May).

Spoilers follow for Line of Duty series six, episode seven...

In the episode, it was revealed that the OCG rat was none other than DCI Ian Buckells (Nigel Boyle), who had hid his rank criminality behind a veneer of shabby incompetence.

Speaking to BBC Sounds’ Obsessed With... Line of Duty podcast, Mercurio said that a clue to Buckells’ corruption was left in the show’s first season, but was overlooked by viewers.

“It was always really important to me that it was someone who had been in season one, someone who had been there the whole time,” he said.

“We did introduce some characters late. Thurwell came in late. Fairbank, the Chief Constable... but I don’t think he would have been a satisfying candidate, because he’d been absent for so long.”

According to Mercurio, the hint came when Buckells allows Dot “The Caddy” Cottan to speak with OCG boss Tommy Hunter in the back of a van, unsupervised.

Ian Buckells (Nigel Boyle) was revealed to have been ‘the fourth man’ all along during Sunday’s finale (BBC)

He said: “It was really about the heritage of the series, going all the way back to in season one, where Dot Cottan says, “Can I just have a quick word with Tommy Hunter in the back of the van?” and Buckells goes, “Yeah, alright”. OK, like, really? Is that what you should be doing? Of course, not.

“You think he’s just a bit rubbish and doesn’t care. But it ends up being part of the character.”

Line of Duty series six can be viewed on BBC iPlayer.