I still have the notepad where I first doodled an idea about MI5 spies. I pitched it to the production company Kudos, which made documentaries: they didn’t have a drama department but the idea appealed. What producer doesn’t secretly want to make James Bond? Channel 4 and ITV said no, but the BBC liked it and we were off.

I grew up in the US and wanted to capture the adrenaline, ambition and scale of American shows. I remember asking: “Can I blow up a car?” The BBC kept saying yes. Back then, spy dramas still had this dark, dour Le Carré legacy. We dared to be shiny.

We had written four scripts when 9/11 happened. The show then became about the people stopping that happening in Britain. Who are they? How do they operate? Spooks was my preferred title. I had considered Five, then the BBC came up with the tagline: “MI5, not 9 to 5.”

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Killing off Lisa’s character with a deep fat fryer was originally going to be in the series finale of season one. We decided to move it to episode two and break viewers’ hearts. It created the sense that nobody was safe. There was a furore afterward but you hardly see anything – it’s all implied. Somebody in LA told me that JJ Abrams screened it for his writers’ room and said: “This is how you do it!”

Advisers who can’t be named were instrumental in keeping things authentic. We’d rip plots from the headlines. Sometimes, the Ten O’Clock News bulletin after the show looked like an extra scene. One episode was referenced in Hansard. After a storyline about an attack on Sellafield with a Scimitar missile, an MP asked: “This TV drama is talking about our defences, why aren’t we?”

The morning after it first aired, I got a call saying ratings were 9.6m and we’d been recommissioned straight away. It was the sort of moment you dream about. MI5 had been having some trouble with recruitment but applications went through the roof. Today’s geopolitics mean you can easily imagine Spooks returning. New threats, a new generation, Harry passing the torch. In fact, I recently had an idea for a festive reboot. Imagine Harry alone on Christmas Day, drinking a rare Scotch. Someone visits with a gift and it gets worse from there …