What happened to Steve Arnott’s back in Line of Duty?

And former star Craig Parkinson has already revealed that he reckons this addiction could play a huge role in the series, explaining on the Obsessed With...Line of Duty podcast: "I’m thinking that he’s slowly upped his drug take and now they’ve taken over him; I think this is going to be a major plot point during this season."

But why has Steve (Martin Compston) been guzzling so many painkillers? And what was the cause of the back injury he sustained in the first place? Well, it all harks back to events in series four of the show, and specifically the attack he suffered at the hands of a ‘Balaclava man’ – a disguised member of the OCG.

That chapter of Line of Duty revolved around an investigation into bent copper DCI Roz Huntley (Thandie Newton) and the murder of forensics officer Tim Ifield (Jason Watkins). Steve was on his way to question Huntley’s husband Nick Huntley (Lee Ingleby) about his wife's whereabouts on the night of the killing when he was attacked.

Making his way to Nick’s office, the lift doors opened to reveal a balaclava-clad assailant who immediately jumped the detective. First smashing his face with a baseball bat, the OCG member then threw the AC-12 officer down a flight of stairs, leaving him for dead.

Later in the series, it emerged that Nick Huntley – whose wife tried to frame him for Ifield's murder – had called criminal lawyer Jimmy Lakewell (Patrick Baladi) when he saw Steve approaching his office. On hearing the news, Lakewell contacted corrupt Chief Superintendent Hilton (Paul Higgins), who promptly ordered a mystery OCG member to attack Steve.

As you probably guessed, the AC-12 detective survived the attack, but the injuries have continually come back to haunt him.

"At the start of the series, by all intents and purposes, he looks like he’s made a full recovery, but as we go through the episodes you start to realise it’s not quite right,” Martin Compston previously teased before series five in 2019.

“There’s stuff wrong with him physically and that’s starting to affect him mentally and this will bleed into the current series.”

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Compston added: “I’m not sure how much we can give away, but in this series there is a certain problem that Steve has physically, which was a bit of an eye-opener when Jed told me about it.

"When you get down to the seriousness of it and how it affects him and his mental health, it turns out to be a very emotional scene.”

We first saw the long-term effects of the fall during the events of series five. Towards the start of the series, Steve was spotted swiping through dating apps late at night before popping a painkiller.

Then, in the series' penultimate episode the problems surfaced again while he was on a date with murder cop and former flame Sam Railston (Aiysha Hart).

His back pain and the side effects of his medication proved a major obstacle when he invited Sam back to his flat – which led to the sad sight of him crying against the bathroom door after refusing to admit what was wrong.

Fast forward to series six and it's clear the effects of the injury are continuing to have a major effect on his life.

In episode two we saw him suffer from a painful spasm while he was visiting Steph Corbett, while at various points we've seen him buy and take huge quantities of painkillers – suggesting a worrying over-reliance on them.

We imagine this will prove increasingly significant as the series progresses...

Line of Duty continues on Sunday at 9pm on BBC One. You can read our Line of Duty episode 4 recap here. Take a look at the rest of our Drama coverage, or check out what else is on with our TV Guide.