The Undeclared War | Preview (Channel 4)

Brand-new cyber thriller from BAFTA-winning creator Peter Kosminsky that lifts the veil on the most urgent battle of our time.

Set in 2024, The Undeclared War tracks a leading team of analysts buried in the heart of GCHQ, secretly working to ward off a series of cyber-attacks on the UK in the run-up to a general election.

When a routine stress test of internet infrastructure goes awry, 21-year-old GCHQ intern Saara Parvin (Hannah Khalique-Brown) suddenly finds herself operating on the invisible frontier of high-stakes cyber warfare.

In a thrilling cat-and-mouse game, Saara and the team at GCHQ must try to stay one step ahead and anticipate their opponents' every hidden move. The clock is ticking as a battle with high stakes and unpredictable enemies takes place entirely online, with very real consequences.

Also starring Simon Pegg, Maisie Richardson-Sellers, Adrian Lester, Alex Jennings, Mark Rylance and Kerry Godliman.

In the opening episode, Saara, a second-year computer science student at London University, wins a highly sought-after work experience place at GCHQ. Her first day coincides with GCHQ's stress test of the security of the telecommunications infrastructure, during which a significant part of the UK's internet suddenly goes down.

Initially thought to be a consequence of the stress test, it is soon shown to be the result of a more deliberate attack.

Saara joins GCHQ's Malware Department, charged with discovering how the virus was unleashed, and quickly finds herself operating on the invisible frontier of high-stakes cyber warfare.

The full series will be available to stream or download for free on All 4 at midnight ahead of the transmission of this episode on Thursday 30th June.