"I think I've always known that Gill was a bad 'un, on some level," Line of Duty star Polly Walker revealed on ITV's This Morning. "But I didn't know to what extent."


In the feature-length series five finale, senior legal counsel Gill Biggeloe (Walker) was suddenly – and dramatically – exposed as one of the four 'H'-es pulling the strings within the police. AC-12 dream team DI Kate Fleming (Vicky McClure) and DS Steve Arnott (Martin Compston) had connected the dots and uncovered her plan to bring down anti-corruption boss Ted Hastings (Adrian Dunbar) by framing him as ultimate top dog 'H' and using the OCG to implicate him for murder.

Gill turned out to be quite the villain – but until the final two episodes, the actress who played her was was kept completely in the dark by Line of Duty showrunner Jed Mercurio.

"I knew two episodes before, what was happening," Polly Walker said. "I knew she was up to no good, but I didn't know to what extent she was a snake."

Line of Duty S5 - Episode 4

That didn't stop Walker from trying to guess what Mercurio was going to do with Gill. The actress explained: "I mean, there had to be a point to her, there had to be reason why she was constantly after Ted. And it never got fulfilled, it was never realised, they never had this affair. But I think people just thought I was a man-eater, some sort of desperate career crazy madwoman."

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Gill Biggeloe survived the series and was given a new identity at the end of the episode, heading off to live in witness protection at an undisclosed location (although, as Irish fans spotted, it looks like she's living on the Seacourt estate in Larne). So could she make a return in series six?

"I think anything's up for grabs. I don't think anybody knows apart from the puppet master, Jed Mercurio. Who knows," Walker teased.

"I think Gill being Gill, my theory, is that she's such a survivor - she won't be playing sudoku in her sitting room for too long. I think she'll be looking for ways to survive, and get on."


The actress also revealed that she hasn't walked a single episode of series five.

"I kind of went into denial mode. I just, it was as if it wasn't happening," she said. "I didn't watch any of it."

But even without Walker tuning in, the tense Line of Duty finale racked up impressive viewing figures - attracting an average audience of 9.1 million, according to overnight figures. The episode peaked at 9.6 million. (To put that into perspective, the UK has an entire population of 66 million people.)


This is the biggest overnight rating for the series ever, and the largest overnight figure for any programme so far in 2019.