A few days ago, the Government sharpened its stock-up-to-survive advice for the nation. The centrepiece of Be Ready! is arguably a checklist of essentials — food, water and kit like a wind-up radio — to cope with severe disruption over three days, from a weather emergency to an all-out cyber attack. Hours after the advice was published, electronic retailer Maplin recorded a 284 per cent jump in sales of torches, a 100 per cent leap in sales of power banks, while radio sales were up 92 per cent — and Iceland recorded a 40 per cent increase in sales of tinned food over the weekend. But London’s prepper community is already stocked and primed. It is time to watch and learn.

Alex lives in a 1950s house in north London with her husband and a rotating cast of three children, ranging in age from 13 to 24. Prepping is her natural default. “I just like to be prepared if anybody pops in.” Covid provided vindication: “When people were running out of toilet rolls, I never dipped below 36. Never do.” Her pull-out larder, cupboards and under-stair storage hold tins bought by the case (usually trays of 12), pasta, rice, eggs and every household essential you could think of. She also has three freezers. “I never go below a dozen eggs or half a tank of petrol either, though I suppose I might need an egg substitute,” she says. Even her jars of dried pasta have “backstage” refill bags. Her husband previously worked for a food charity and rotates the stock. “I do the buy-in, he does the clearing.” She says she doesn’t write lists but has an uncanny ability to picture a shelf or cupboard instead and know the gaps. It sounds like the prepper’s form of synaesthesia — when some musicians see colours when they hear certain notes. “If I dip, then I replace it,” she says.

She shuns upscale survivalist kit. “I couldn’t have expensive stuff not being used.” Recently she was “gutted” to miss a £15 Lidl solar charging station, which sold out before she got there. She currently has 12 litres of water (“not enough”) but has several suitcase-sized containers in the garden ready to fill from the tap. Last month she filled one and drove it over to a relative’s when their mains water failed. (“A dry run, or should that be a wet run?”) Her camping stove is out on loan, but she reasons they could cook on the fire pit. All in all, how long could she manage? “I could look after my lot for three weeks, pushing four.”

This is well above average. Government advice starts with three days, but a Cabinet Office survey this year found a quarter of Londoners believed they could manage no more than a day without utilities.

Craig* lives on the ninth floor of a block in Lambeth with his partner and young child. The Government’s three-day specification doesn’t impress him — he thinks of survival in months and years. He previously lived in Australia, where he found more off-the-shelf “prepper products”, such as tubs of freeze-dried emergency meals. Instead, he uses catering buckets and fills them with heat-sealed Mylar packets of food. The bottom row of a large Ikea bookcase against one wall of his living room is full of neatly labelled buckets containing rice, lentils, beans, pasta and oats. The other shelves are stocked with hygiene products, wind-up electronics and torches, many of which he acquired in Covid but tests frequently. The top row is now reserved for nappies, formula and Calpol. “Since Covid we’ve had a baby so this is new.” His must-have item? Eight rolls of black bags: “Rubbish collections would stop.”

He covets Costco’s 940-litre pallet of Kirkland Signature spring water, currently on offer for £299.89, or 32p a litre — as do many preppers. But his partner has vetoed it on the grounds that there is too little space for 1,880 bottles. For now, he is making do with a “small” stash of 20 litres of water and a 3.8-litre gravity filter bag, which can be filled with untreated water, drawn through a filter without the need for electricity.

Food researcher Professor Paul Behrens lives in north London with his partner. He began putting food away recently while working on the National Emergency Briefing, a public information initiative that focused on how extreme heat was disrupting supply chains. He has two months’ worth of supplies tucked into a dedicated cupboard: oats, rice, pasta, beans, nuts and olive oil, accumulated by buying a little extra with each shop. While prepping gets a bad rap as a selfish pursuit, he thinks it’s important to consider the “pro-social” aspect. If supplies are disrupted, he won’t need to join the rush on supermarkets, leaving more for those who need them.

London’s prepper scene is a broad church, running full spectrum from casual acquisition to deep survivalism. I’ve come to think of it as a colourful orchestra, each playing to their own fears, circumstances and budgets. But as millions more potentially join, this orchestra could do with a conductor.

Animator Dom Brooks could be that conductor. He’s created the Provision app, which you can download for free. Brooks and his wife have two young children and keep emergency supplies in a large garden box in the loft, a habit they acquired during Covid. He developed Provision after tiring of climbing upstairs to check expiry dates and because “everyone hates spreadsheets”.

In part it’s a sophisticated stock manager. You input the members of your household — including pets — and then your existing supplies, either manually or by scanning barcodes. It will calculate how many days worth of food, water and essential medication you have, identify what is likely to run out first and flag approaching expiry dates. You can use the app to work out the gaps, generate a shopping list and replenish supplies through shopping links — principally on Amazon, where Brooks can earn money from affiliate links. It can also monitor local weather warnings.

But if disaster strikes, provided you have enough phone battery, you’ve also got an apocalypse manager to hold your hand. If London’s taps run dry, it switches from preparation to managing your reserves via its offline inventory. In short, it’s designed to help you make decisions as an emergency unfolds.

How much would it cost to stock up like this? Following Provision’s guidance, 90 days’ worth of food and water for one person would come in at about £300, or £750 including equipment. For a family with two children, it’s approximately £850, or £1,760 with equipment.

That’s a big outlay. Does the threat level merit this? It’s a question that can feel like an impossible cost-benefit analysis, as if each household must triangulate the distance between a wholesale cyber attack and investing in a tonne of water from Costco.

Professor Washington Yotto Ochieng, head of the Centre for Active Resilience and Security at Imperial College, describes London’s threats as a pentagon diagram: cyber attacks, physical threats, social disruption, environmental hazards and biological emergencies form each side. Increasingly, these threats intersect. A flood might coincide with a cyber attack on healthcare, for example. Yes, folks, we’ve got it all! London depends on interconnected transport, energy, water and communications networks. As systems become more digital, “the actual surface area of attack is increasing”. Ochieng also believes London has lost some of its preparedness culture, because we’ve enjoyed “relative calm”.

Most of us will begin the fight back to resilience with food. Tim Lang, emeritus professor of food policy at City St George’s, University of London, has shaped Britain’s thinking on food security, including London’s preparedness for disruptions to its food supply. He is not a fan of the word “prepping” for starters — “Oh, don’t use that Lucy!” — preferring “civic food resilience”. His misgivings are not merely linguistic. “Where are people supposed to put everything? How can families struggling to afford food build reserves? What use is a freezer during a power cut? And what happens after three days?” These are all good questions.

“You can’t expect individuals to resolve the fault lines of the food system,” he says. Our ultra-efficient, just-in-time food system has, according to Lang, made us incredibly vulnerable. The whole country depends on 131 major distribution centres; Tesco alone moves its food through only 20 hubs. Knock out enough of these and supplies are in serious trouble. In London, where 30 million meals are served daily, Lang’s work has uncovered a food system so complex nobody had a complete picture of how the capital was fed.

“The big shocks to the food system will not be resolved by us storing food,” he says. But even Lang, who lives with his wife in central London, keeps an emergency pantry. It contains “30 enormous jars of beans and chickpeas, dozens of baked beans, 24 tins of tomatoes, sardines and dried fruit. We only store food that doesn’t need to be cooked,” he explains, although there is also rice and dal, a legacy of his childhood in India, and dried pulses. These require heat, but he has no camping stove. He worries about keeping gas canisters indoors.

José Escribano, a disaster-response and evacuation researcher at Imperial College, emphasises that preparedness offers psychological benefits, including a sense of control. This “avoids despair”, which can lead to us making worse decisions in an emergency moment. This is backed up by studies showing that the belief we can take effective action is a key determinant of success once a disaster hits.

But I wonder — what else effective action might look like? Could London prepping, like our threat risk, have a larger surface area too? On Zoom, Suzanne from Earlsfield cradles a homegrown squash, wider than her shoulders. Suzanne considers herself to be a community resilience builder, connecting people and skills — not a prepper. But it does seem like she’d be handy in a crisis. She has saved water from her dehumidifier in huge bins in the garden that would be used to flush the loo if needed.

I return to Ochieng and ask how he approaches prepping. He says he is adding supplies to his monthly shop and storing them in his garage. But that’s not his priority. What is? “The thing I need to do is to get to know my neighbours, because the next time something comes up, at least then we know what to do as a community.”