Today’s TV dramas require ever more complex story­lines to attract and satisfy increasingly sophisticated audiences. Yet writers cannot make their thrillers too complicated, or confused audiences will switch off.

This writing dilemma has been successfully negotiated several times by Jack and Harry Williams. They have pulled off the delicate balancing act once again with the second series of the acclaimed ITV show Liar, which is co-produced by SundanceTV.

The Williams brothers knew that the very title of their six-part project would suggest a convoluted plot that questioned which characters were lying and who was telling the truth.

But the theme of constant lying can be both a blessing and a curse, according to Jack Williams. “Our story is about people hiding secrets from themselves, their spouses, their family – and I think that worked well in the first series,” he said. “We definitely tried to do it again in the second series because, with people lying, you also have the expectation of them being found out. Of course, then other things happen.”

Always at the back of their minds while writing is the need for clarity. “The story has to be clear to the viewer because we haven’t done our jobs properly if they don’t follow it,” said Harry Williams during the Q&A session following an exclusive RTS screening of the first episode of series 2.

The brothers’ confidence in negotiating the complexity issue is well-founded because, not only had they already jumped that hurdle in series 1, but they were also similarly effective in another of their thrillers, The Missing. This drama developed dual timelines and multiple plots, a structure that creates puzzles which they both enjoy solving.

“Our rule about structure is really just a case of how we tell the story in the best way,” explained Harry Williams. “If you can tell it in one time line, then fine, we would do that. We’re not attemp­ting to be clever for the sake of it.”

The first series of Liar centred on an allegation that surgeon Andrew Earlham (played by Ioan Gruffudd) raped teacher Laura Nielson (Joanne Froggatt), but it was unclear who was telling the whole truth. The series ended with a shot of Earlham’s dead body lying prostrate in a marsh. The new series picks up from there.

"It takes ages to look at every version of an ending but, finally, you have to be led by the story"

“We had to tell the Liar story in two timelines,” said Jack Williams, “because it’s important that you see what’s happening to Laura in the present day and also how it happened. Every time we go back in time and see what Andrew did, it’s a whole other level of intrigue.”

Yet a second series – which took nine months to write – was not originally an automatic option. “We explored a lot of endings for series 1. But if we’d ended it with Andrew just going to prison, it would’ve been shit, so killing Andrew was the best way to end,” said Harry Williams. “In the writing process, it takes ages to look at every version of an ending but, finally, you have to be led by the story and, for Liar, we needed more time to tell everything.”

The first series became a talking point because it was broadcast as reports were emerging about allegations of rape by Harvey Weinstein and his criminal treatment of women.

The programme, its writers and star Joanne Froggatt were caught up in questions from the tabloid press and the Twitterati concerning whether it was legitimate to have a storyline based on a woman being raped. But Froggatt was always adamant that the series was not using sexual assault gratuitously.

“No, that wasn’t the case at all,” she said. “When our first season aired, sexual assault against women was a subject that seemed very taboo. Yes, sexual assault as a crime is what starts the thriller process in Liar, but audiences accept shows based on murder, child abduction, paedophilia, so why aren’t we talking about sexual assault as well? If we do that, then it becomes less of a taboo subject.”

She added: “The series made people look at themselves and question how they judge other people, especially those who’ve been in these awful situations that we haven’t experienced ourselves.

“Why is anyone then qualified to judge them? In my eyes, I’m not. That’s what hit home with people: the series had something to say in the background without hitting people over the head with it. That’s why I wanted to do the project to start with.”

Answering a question on the value of intimacy co-ordinators, Froggatt said: “Our first season aired two years ago, so the #MeToo movement hadn’t happened and there were no intimacy co-ordinators, but they do have them now and it’s a great idea.

“It’s as normal now as having a stunt co-ordinator. In the past, when I’ve had to do an intimate scene, I’ve always treated it like a fight scene because they’re similar. As actors, it’s our job to make these things look natural.”

"The series made people look at themselves and question how they judge other people, especially those who’ve been in these awful situations that we haven’t experienced ourselves"

She said that acting sex scenes was similar to choreography: “I have conversations with the other actor and the director, telling them that this is the way I want to do it. That’s how I’ve always done it myself. It’s about creating a safe space.”

She explained that Jack and Harry Williams were very keen for their actors to be in control of these scenes. “We had a great team of people and I’m very fortunate to say that any intimacy scenes have always come from a place of respect, openness and discussion.

“Plus, Jack and Harry write so well for women, anyway. They were open about saying to Ioan and myself that we could change anything if it didn’t feel right or if we felt uncomfortable. The intention of Jack and Harry was never to show violence against women on screen, it wasn’t to be a salacious show. It was to raise questions in people’s minds and I’m really proud of that.”

For the other female star of the series, Katherine Kelly, there was a different kind of challenge: introducing a new central character into an already successful show. She said that she did a lot of the preparation for the part of the uncompromising Detective Inspector Karen Renton: “I didn’t want her just to be a narrator. She had to be an important and authentic part of the story, someone you believed was the only person who could solve the case.”

Kelly helped to decide that her character would show no favour to the rape victims or to any other character. “I discussed who she was with Jack and Harry, about her not being emotional, and her feeling that it would be unprofessional for her to have empathy or sympathy for these people. It was an interesting character to play, because you don’t see many cops brought in at this stage of a show when the audience already has sympathies for the characters.”

But neither Froggatt nor Kelly need worry about how to adapt their characters for a third series of Liar – the Williams brothers have absolutely no plans for that. “Yes, series 2 was about working out who killed Andrew, but it was also about getting more under the skin of the characters and finding out how they tick, going deeper into the story. But series 3? No, there’s a definitive, and very satisfying, ending to series 2, so that’s it, no more.”

The RTS screening and Q&A of Liar was held at the Curzon Bloomsbury in central London on 27 February. The event was produced by the RTS in conjunction with IJPR.