We are at war. Four words that sound ludicrously melodramatic on a sunny spring day, when all may not be exactly right with the world – but when you can still shut your eyes to a lot of it just by switching off the news and cracking on with life. No bombs are falling, no bullets flying, no sirens sounding. Though the idea that Britain is already under a form of hybrid attack is commonplace in defence circles, politicians still mostly skirt around it; and it was jolting at first to hear the Labour MP (and former RAF wing commander) Calvin Bailey make the case for conflict being our new reality at a conference hosted by the Good Growth Foundation thinktank last week in London. But then he started to unpack his reasoning for why war is no longer what you think it is.

If war can be considered an assault on five fronts – against a country’s political leadership, critical infrastructure, essentials such as food or fuel supplies, civilian population and armed forces – then Britain is arguably now being attacked on the first four without a shot being fired. Think of rampant, Russian-generated political disinformation on social media and attempts to bribe British politicians; of Russian submarine surveillance of the British undersea cables carrying most of our internet traffic, or the four “nationally significant” cyber-attacks recorded every week; of the blockading of food and fuel supplies through the strait of Hormuz. Think, too, of Keir Starmer’s warning in the Sunday Times last week of conflict with Iran coming home to British civilians via “the use of proxies in this country”. He didn’t elaborate, but counter-terrorism police say they are investigating whether a spate of arson attacks on synagogues, Jewish-owned businesses and Iranians living in Britain may have been sponsored by Tehran – a thugs-for-hire tactic familiar from the Russian playbook for sowing division and hate.

Whoever may be to blame, such attacks fuel the fear that Britain isn’t safe either for Jews or for Iranians seeking sanctuary here, while simultaneously feeding an insidious far-right narrative that immigrant communities can’t peacefully coexist. Add all this together and you potentially have a highly deniable form of shadow warfare involving weaponising a country’s own weaknesses and prejudices back against it, while stopping short of causing casualties. Bailey, who led the RAF evacuation flights from Kabul as it fell to the Taliban in 2021, doesn’t seem the type to panic. But in a recent essay for the Fabian Society, he argues that Britain should be prepared for escalation.

It’s 10 months since the strategic defence review, commissioned by the former Labour defence secretary George Robertson, similarly argued that Britain must urgently equip itself not for the expeditionary foreign wars against non-state actors we’re used to fighting alongside the US, but for homeland defence against a well-armed peer country in a sustained conflict. To strip away the jargon: if when you imagine Britain at war, you think of the Iraq and Afghanistan conflicts, you’re out of date. The next big war may come uncomfortably closer to home, be fought from necessity not choice – and be less about serving as the US’s willing poodle than about poodles facing the consequences of a master going rogue.

Forgotten in the resulting row over how to find more money for defence – to which Bailey’s answer, incidentally, is a mix of new instruments for borrowing and reforming procurement – is Robertson’s call for a national conversation, levelling with the public about what exactly all this means in practice.

After much public prodding, Starmer seems now to be engaging, though arguably too little and too late for the review’s frustrated authors. As I write, Robertson and his co-author Fiona Hill are due before a parliamentary committee on the national security strategy, while Hill is expected to spell things out more bluntly in a lecture on Wednesday.

Despite seeing the damage that cheap, mass-produced drones can do in Ukraine and across the Gulf, she warned last week, Britain still isn’t properly prepared for a drone flying through the window of a strategically important building. Our overstretched NHS may not be able to handle mass casualties – and we lack the stockpiled food supplies or analogue backups to digital systems that would help us ride out a successful cyber-attack or serious act of sabotage. Preparing for this unfamiliar form of attack isn’t just about buying tanks and fighter jets, but also about two things that most Labour voters probably expected a Labour government to do anyway: shoring up the public realm to cope in a crisis, and forging a more mutually trusting and tolerant society that is resilient to extremism, where neighbour does not fear neighbour and people willingly help each other in a crisis.

Starmer hasn’t found the words to articulate any of that yet – and if May’s anticipated local election drubbing is bad enough he may not be here to make the case for much longer. But anyone with ambitions to succeed him must be able to show both that they are capable of leading a country under attack, and of explaining the puzzling nature of that attack without inducing panic to a public heartily sick of being asked to make sacrifices. A war this hard to discern, even when it’s supposedly upon you, may not feel yet like much of a threat. But lives may in future depend on seeing clearly into the shadows.

• Gaby Hinsliff is a Guardian columnist