Gemma Whelan on The Tower, taking tips from Suranne Jones, and filming at 9 months pregnant

With her due date just three days away, she returned to shoot some scenes (shot with clever camera angles) in south London, close to where she lives. But, she says, if it had come to it she “would have gone to Liverpool”, where the rest of the ITV series was shot. “They've got hospitals up there. I just thought, ‘If the baby comes, the baby comes’. But I didn't think for a second I would say ‘no’. I wasn't poorly. I was just pregnant.”

In the event, the baby was late. “I finished filming on a Tuesday, I think it was, and Freddie came the next Tuesday."

Professionally, The Tower marks a new chapter for Whelan. The actress is best known for highly memorable supporting roles in the likes of Game of Thrones (as Yara Greyjoy of the Iron Islands), Upstart Crow (as Kate), and Gentleman Jack, as Suranne Jones’ on-screen sister, Marian Lister.

However, in The Tower, Whelan is front and centre in her first primetime leading role. She plays DS Sarah Collins, a compassionate detective in an orange coat, and whose rise in the ranks has been unfairly stymied because she “can’t tell jokes to men in bars”.

I ask Whelan if she took any inspiration from former co-stars such as Jones or Emilia Clarke (Game of Thrones’ very own Queen of Dragons) when it came to leading a TV series. “Certainly with Suranne – I very rarely worked with Emilia, but with Suranne [I worked] daily for many months. I guess her work ethic really rubbed off on me: her prep, the way she led the team – inadvertently, you know, she's not trying to lead, but just her attitude on set and the way [she had her] lines really prepared.”

DS Sarah Collins first appears on-screen dressed in a lilac shirt beneath the (already trademark) orange coat. The colourful ensemble had a dual purpose: firstly, ensuring viewers could easily spot the character from among a crowd. “There was a ‘no blue’ rule on our set,” Whelan jokes. “I think Sarah's outfit certainly says [she's] unconventional, different – ‘slightly nerdy’ was what we were going for, you know, she's not cool and stylish. And she's not afraid.” What’s more, “having a big coat when you've a growing belly is quite helpful”.

When we first meet DS Sarah Collins, she’s just arrived at a crime scene. A veteran beat cop and a teenage girl have fallen to their deaths from the top of a tower block in south east London, and in mysterious circumstances. Sarah’s job is made infinitely more difficult when the key witness, rookie police officer Lizzie Adama, disappears hours after the incident.

As Sarah searches for Lizzie, she’s also hindered by suspect male colleagues who belittle her, attempting to undermine her case by claiming she’s under stress following a painful break-up with her ex-girlfriend. “She's not manipulable, thankfully,” Whelan says of Sarah. “She's tough and she's able to compartmentalise, and I relate to that. I think many women will relate to those things.”

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The series is based on Post Mortem, the first in Kate London’s Metropolitan series of novels, which centre on the characters of Sarah and Lizzie. When it came to casting an actress in the role of Sarah, Whelan was the author’s first choice. “It's very flattering, isn't it?” Whelan says now. “Yeah, I was thrilled, and when I read the script it just felt like a fit, it really did. I hope that doesn't sound arrogant!”

Whelan related strongly to the character, sharing a “moral compass” that “is very, very black and white”. As an example, she mentions how she felt compelled to warn ITV about her then-very early stages pregnancy before signing the contract.

But Whelan also related to the loneliness Sarah experiences. “I related to a lot of the things that she's going through, and even in my personal life - things are very different now, but you know, I related to a former version of myself that was possibly a little lonely and vulnerable in my private life and really threw myself into work.”

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The role is one Whelan would be keen to reprise for a second season. “All of us are hopeful that we might get a second series. It certainly depends, obviously, [on] ... how it goes down and stuff. But I know Kate's got three books and is writing a fourth.”

I mention my conversation with Whelan’s co-star Tahirah Sharif (Lizzie), who teased that The Tower will shine a light on police officers' unconscious biases. “Yeah, I think it could be interesting because, of course, they're under the spotlight for not good reasons at the moment,” Whelan says.

Over the course of the TV series, several officers follow their own personal codes (sometimes flying in the face of the rules), with varying degrees of success. For Whelan, it's all about getting viewers to ask questions of themselves. “I think it's a good jumping off point for people to ask, ‘What would you have done?’”

The Tower airs on ITV at 9pm on Monday 8th November.

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