Who is Chief Constable Philip Osborne in Line of Duty?

In the first couple of episodes, Osborne appeared in key archive footage relating to the Gail Vella investigation, and his significance to the plot only increased in episodes five and six with some major new revelations.

But who actually is Osborne? And what significance does he have to the series? Read on for everything you need to know.

Who is Chief Constable Philip Osborne?

You have to go all the way back to the very first episode of the very first series for Osborne's first appearance on the show – when he was introduced as the leader of the Counter Terrorism Unit of Central Police, where Steve Arnott was working at the time.

From his first appearance, Osborne was a shady character, seen telling members of the Strategic Firearms Command, including Steve, to lie in court after they had mistakenly gunned down a suspect, Karim Ali.

It was Steve's refusal to take part in this cover-up that led him to be dismissed from the department on Osborne's orders and move to his job at AC-12, so in some ways, he is actually responsible for setting the whole series in motion.

He did not appear again until the series one finale, when he was brought in to help investigate a possible terrorism angle in the murders at the Borogrove Estate.

He was seen to have rather a chummy relationship with Chief Superintendent Derek Hilton (who we now know to be corrupt) and later clashed with Arnott, who explained that he believed there was no terrorist involvement and also took him to task for his role in the earlier cover-up.

During the series one epilogue, we were informed that Steve had gone on to testify against his ex-colleagues and Osborne, but no charges had been brought forward nor any prosecutions made.

That was the last we saw of Osborne for a while, until this season six – in which he has twice appeared in archive footage being reviewed by AC-12.

First, in episode two, he was seen giving a statement to the press during the inquest into the Karim Ali shooting. It was at this point that Ted revealed that Osborne has now been promoted to Chief Constable – so clearly his part in the cover-up has had no lasting effect on his career progression!

Then, we see him again in episode three, this time in previously unaired news footage in which he is being interviewed by Gail Vella.

Their exchange centres on a question relating to police recruitment figures, with Vella explaining that the Force is 100 officers short, causing Osborne to dismiss her faulty figures.

But Vella then reveals that her figures had been sourced from police records, which promoted him to storm away, preventing her from following and continuing her line of questioning.

Then in episode four, DCC Andrea Wise explained to Ted that it was the Chief Constable himself who was ordering the merger between the forces various anti-corruption units.

We heard some more from Osborne in episode five, again via news footage, with the Chief giving a statement that accused the PCC and anti-corruption units of undermining the efforts of the police by sowing public distrust.

This in turn led to a crucial scene in which PCC Sindwhani informed Ted that he could no longer stay in his role, as Osborne's continued crusade against the anti-corruption units put him in an extremely difficult position.

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And then came the revelation: it transpired that Osborne was on the same team as Ian Buckells (Nigel Boyle) and newcomer Marcus Thurwell (James Nesbitt) that had been in charge of the bungled investigation into the murder of Lawrence Christopher, the very case which Gail Vella had been looking into prior to her murder, potentially giving Osborne a motive for the killing.

Furthermore, later in the episode he took the decision to fast-track the anti-corruption merger by bringing in AC-3 boss Patricia Carmichael, who immediately scrapped some vital surveillance operations, which also doesn't exactly reflect well on the Chief.

Despite not appearing much in the penultimate episode, suspicions of Osborne only increased further during the interview scene with Joanne Davidson – with Ted rather forcefully asking her "Is it the Chief Constable?” Jo didn't answer affirmatively, but she was clearly intimidated by any mention of 'The Fourth Man' so we can't read too much into her 'no comment'.

And Osborne's speech at the very end of the episode also did little to dispel suspicion. “For too long now, police officers have had to serve faceless, unaccountable bureaucrats," he said.

"We’ve even had to suffer political opportunists, trying to win votes by vilifying police officers with false allegations of corruption. We must defend this constabulary from those who would obstruct us in serving the public.

"Not only does this force face enemies without, there are enemies within. I will personally see to it that those enemies within are made to suffer the consequences.”

As usual, he is very determined to downplay allegations of corruption – a little too determined perhaps? Especially given his promise to make his enemies – presumably AC-12 – "suffer the consequences".

Despite all this though, one person is convinced Osborne is not guilty: Patricia Carmichael. Indeed she even made DC Chloe Bishop take his picture off Ted’s pin-board and put it through the shredder!

So what exactly is Osborne's significance in all this? He's clearly bent in one way or another, but is he connected to the OCG and the broader corruption plot within the Central Police?

Well, given his past record of dodgy behaviour, his rise to the very top of the Central Police Force, his clearly antagonistic relationship with Gail Vella and his general disdain of AC-12, it's certainly possible...

Line of Duty continues on Sundays at 9pm on BBC One. Take a look at the rest of our Drama coverage, or check out our TV guide to see what’s on this week.