On the set of The Whistleblowers, in a grimy, disused warehouse somewhere in East London, the atmosphere crackles like a high-voltage electrode, freshly charged for ghastly torture.

Forgive the simile. But given the subject matter of the first episode of Tony Marchant’s gritty new thriller series for ITV – the illegal imprisonment and abuse of terror suspects in the UK – it seems somehow appropriate.

This is not a series for the fainthearted. By the end of the first episode you will have witnessed a barefoot, badly beaten man being bundled into the back of an unmarked vehicle. Later, too, you will watch him being “water boarded”, which the torture cognoscenti will tell you is a process by which the victim is tied to a table, his face covered with a cloth while water is poured constantly over his face to induce the sensation of drowning.

“That scene is very shocking, but it’s also revelatory,” Marchant says. “It was important to show that water boarding is the torture of choice in terms of detainees. I wanted to make the audience feel as uncomfortable and claustrophobic as the victim.”

Good old Marchant. He never was one for letting his audience off the hook lightly – think of the recent Mark of Cain, about soldiers abusing their powers in Iraq, or Holding On, the award-winning series about London life in the 1990s, which was memorably described by one critic as “TV to commit suicide by”.

“But then drama is not about people being happy,” he says. “It’s about people being miserable. It’s about things not being normal.”

His work tends to be marinated in social issues, questions about morality and what it is to be human. The Whistleblowers, too, has many of these hallmarks. “The last thing I want to be seen as is an issue writer,” Marchant says. “What could be more dull than getting on a soapbox and telling your audience to eat its greens? It would never work.”

The Whistleblowers marks Marchant’s first sortie into the thriller genre. In each of the six episodes our two protagonists, Ben Graham (played by Richard Coyle) and Alisha Cole (played by the Romestar, Indira Varma), investigate corruption, injustice and nefarious practices in various companies, organisations and institutions. Included are the pharmaceutical industry, academy schools and the immigration authorities. At the same time they are resolving conflicts in their steamily passionate private lives, including an unplanned pregnancy, written into the script when Varma discovered that she was expecting in real life.

As always in a Marchant drama, the research has been meticulous. Indeed, the writer based the whole concept of the series on a real-life agency that helps whistleblowers, which he consulted extensively.

He wrote three of the episodes himself, but also handed one over to the writer Paul Logue and the other two to real-life whistleblowers, Tony Saint, a former immigration officer, and Steve Thompson, a former teacher. “It helps if you know the world that you’re writing about,” he says.

For all that, Marchant doesn’t claim that the series is docudrama or that any of the stories are based on real cases. “I would find the whole docudrama medium far too restrictive,” he says. “As a writer I like to use my imagination to create plausible ‘what if’ scenarios.

“In episode two, for example, we take a look at the pharmaceutical industry and imagine a company creating a pandemic for its own gain. “You and I are talking about it now at roughly the same time as a research lab has unwittingly released the foot-and-mouth virus into the environment. This is bad news for farmers and their animals, but good news for the viability of this drama. It shows that it has real topicality.” Not that Marchant is blowing his own trumpet, or indeed, whistle here. He simply hopes that his audience will tune in, be entertained, moved, amused at times and, perhaps, take some time out to think about the issues. “That’s really all you can ask of any drama.”

The Whistleblowers, Thur, ITV1, 9pm

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