Are we ready for war? Welcome to The i Paper’s opinion series in which our writers tackle a grim question that, until recently, few had thought to consider.

• Ray Mears: This is the golden rule of preparing for war
• I’ve seen the state of our weaponry – helping Ukraine has left us exposed
• Our nuclear weapons are no longer enough to keep us safe
• Not enough people want to die for Britain – and who can blame them?
• ‘Little green men’ and ghost fleets: How Russia could drag us into war before 2030

There’s a term for a devastating cyber-attack on a broad range of fronts, hitting all the things that make modern life possible, from banking to the water supply: “the everything, everywhere, all at once attack”. These scenarios sometimes seemed a bit hysterical: the power grid, for example — the first target in any cyber wargame — is difficult to hack into. But advances in quantum computing and artificial intelligence mean that the everything, everywhere, all at once attack will one day be possible. And Britain isn’t ready.

Quantum computers are astonishingly good at some kinds of calculations. They can make all the many wrong answers to break a code fade away almost at once. Ordinary computers have to check every single possibility one by one – they would need trillions of years to crack the so-called public key encryption that locks down the internet. In theory, a quantum machine could do it in a few hours, even a few minutes. Public key encryption is used on every secure web page, every time a password or other secret is sent over the internet. Most of our vital systems are networked. Power, water, transport, banking, manufacturing, healthcare: they would all be vulnerable.

Dr Carsten Stöcker is a German scientist and tech entrepreneur whose company, Spherity, makes “post-quantum” software. He warns that autonomous AI agents, using passwords cracked by quantum computers, would be able to carry out attacks on a scale and at a velocity never seen before. Those who wish us harm – whether nation states like China or Russia, or criminal groups – would no longer be limited by human speed or even the speed of classical computers. “Our life depends on the internet” he tells me. “The security of the entire internet will break. This can be an existential crisis.”

So, what could an attack look like?

The day begins with a near miss at........

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