On the day that London drowned, 16-year-old Shirley Orchard was serving customers bars of chocolate and packets of cigarettes at her father’s shop on Canvey Island. The town, which sits on the underbelly of Essex, where the North Sea becomes the River Thames, had been teased by bursts of showers and sunshine throughout the day. By dusk the clouds had squeezed themselves dry. Orchard served her last customer of the day: a woman who, after seven years of trying for a baby, had recently given birth. After Orchard had closed up the shop, she began to walk home, her stride stretched by a chasing breeze.

The wind had been whipped to life two days earlier by a depression off the south-west coast of Iceland. From there, it began its journey towards Scotland. Soon after first light, on 31 January 1953, the captain of the ferry Princess Victoria ignored a storm warning and set sail from the Scottish port of Stranraer. As the ship – heavy with cargo, crew and passengers – cleared the mouth of the sheltered Loch Ryan, huge waves butted and then breached its stern doors. At 2pm, the order came to abandon ship. One-hundred-and-thirty-two people died, including the deputy prime minister of Northern Ireland and every woman and child aboard.

At first, the storm appeared to be heading on towards Denmark. Then, unexpectedly, the North Sea winds aligned with a rising spring tide and, instead, shooed the squall down England’s east coast. When surge water breached the Wash, the square-mouthed bay in East Anglia, authorities in Lincolnshire attempted to issue a flood warning to caution cities likely to be affected. The message never left the county where now, in patchwork fields and under scribbles of wire, telephone poles lay toppled. The storm battered unwitting coastal towns in Suffolk, Essex and Kent. Fifteen people drowned in King’s Lynn, Norfolk, when a six-foot wave burst through the town centre. In the nearby seaside town of Hunstanton, a train was forced to stop because of bungalows on the line.

Further south, in Canvey Island, Shirley Orchard awoke to screams from the houseboats moored in the creek at the end of her road. Canvey Island had long been considered flood-ready. But after centuries of reinforcement, its protective walls failed – 141 million gallons of water, backed by shrieking winds, mounted the blockade.

Residents who attempted to flee were struck by shoulder high seawater, timber, dustbins and other debris. Orchard and her family sheltered upstairs. Those staying in nearby bungalows were trapped. Some punched holes through the ceilings of their buildings and climbed on to the roofs, pulling their children after them to escape the torrent. Fists bloodied, they then huddled for warmth, and waited to be rescued.

At an event held to mark the 60th anniversary of the flood, Orchard recalled how she fled Canvey Island in the middle of the night on the back of an army truck during an evacuation of 13,000 residents. Elsie Foster, the mother that Orchard had served just a few hours earlier in the shop, and Foster’s husband, Ernie had died in each other’s arms. Their eight-week-old baby, Linda, was found alive in her bobbing pram.

The storm tide hastened towards the capital. At midnight, the BBC broadcast a message from the police, warning of an “exceptionally high tide” in the Thames. Cars equipped with loudspeakers were dispatched from New Scotland Yard to issue flood warnings in the streets, followed by reserve motorcyclists who blew whistles to alert people to the danger.

At London Bridge, in the early hours of the morning, the water reached its highest level ever recorded, six feet higher than anyone had predicted. Higher than the surge that flooded the Tate gallery and drowned 14 in 1928. Higher than the 1809 flood, when the central arches of Wallingford Bridge collapsed. Higher than the December flood of 1663, in which, according to Samuel Pepys, “all Whitehall … drowned”. Higher than the flood of 1236, when people were seen rowing in boats through the palace of Westminster.

The water reached the top of the parapet that runs along the Victoria embankment, where tourists now photograph one another beneath the spokes of the London Eye. Then, unexpectedly, the wind turned and the surge began to retreat. At 4.36am, New Scotland Yard issued a new instruction: “Danger of flooding now past, notify public accordingly; withdraw watchers and loudspeaker cars.” By morning, across Britain more than 40,000 people were left homeless and 160,000 acres of agricultural land had been ruined by saltwater; 9,000 sheep had been killed, along with 34,000 poultry, 2,600 pigs, 1,100 cattle, and 70 horses; 531 people were dead.

In the aftermath of the storm, which came to be known as “The Great Tide”, lavish measures, such as the £534m Thames Barrier, were implemented to protect London and its surrounding counties. We slept easier. The storm faded from the nation’s collective memory. Few Londoners today know that the capital was the site of a natural disaster of such magnitude. Seven decades on, however, government commissions, scientists, futurologists and people once considered wild-eyed scaremongers are converging on the view that floods of 1953 levels of severity are likely to become commonplace.

The global temperature has risen by 1C in the past century. Fourteen of the hottest years on record occurred in the past 15 years. And 2015 was the hottest since records began in 1880. Individual countries will feel the effects of the change in individual ways. Saudi Arabia will have to contend with stronger and more frequent heatwaves. Bangladesh risks being wiped off the map by rising sea levels. The sea that surrounds Britain is expected to rise by up to 50cm in the next century, a change that poses obvious risks for an island. But perhaps the biggest worry is that it will get a lot wetter.

This seems counterintuitive. Why, as the world grows warmer, would Britain grow wetter? As temperatures rise, ice caps melt and the amount of water vapour in the atmosphere increases, so too does the risk of “intense precipitation events”, the scientific jargon for heavy rain. The latest government figures state that the likelihood of floods in the UK has almost doubled in the last century.

We do not need to take their word for it. In 2007, flooding in Britain affected 55,000 homes and killed 13 people. In December 2015, floods caused by the amiably named storms Desmond and Eva caused £175m worth of damage to homes and businesses in Cumbria. The public bill for fixing the infrastructural wreckage – the broken bridges and ruptured roads – is currently estimated at £250m. Dredging rivers, deforestation and unchecked housing development in floodplains may have exacerbated the human cost of Britain’s floods, but climate change is responsible for the rise in extreme flooding events. Worse is to come.

The River Thames at Putney in west London during the flood of 1953.

Photograph: Daily Mail/REX/Shutterstock

Lord Krebs is a chairman within the Climate Change Committee (CCC), a group commissioned by the government to, in part, evaluate the environmental risks we now face. Krebs is so assured of the UK’s unpreparedness for disaster, that, in an interview on Radio 4 in December, he issued an urgent warning. “The biggest single risk from climate change for this country is the increased likelihood of flooding,” he said. “The government needs to rethink its whole strategy of managing flood risk. Our money should be going into flood protections and doing everything to protect the vulnerable land beneath sea level. There is so much of it.”

On 12 July, Krebs’s team will publish a crucial report – one that will surely struggle for attention thanks to the prospect of more immediate disasters – which outlines the most urgent risks that Britain faces from climate change. The risk assessment report draws upon three years of research and analysis, involving hundreds of academics and scientists. Some of the research seen by the Guardian puts the current cost of UK residential flood damage at £340m per year, a figure that will rise to £428m as the average global temperature rises by 2C, the limit that numerous world leaders agreed upon in December at the 2015 United Nations Climate Change Conference, held in Paris. The experts consulted by Krebs’s team claim that 180,000 more British homes will be at risk of flooding by 2050.

According to this research, around 20% of the total length of coastal defences in England, which protect around 2m homes at risk from sea flooding, could be vulnerable to failure if sea levels rise by just half a metre. A one-metre sea level rise around the British coast will place 2,000 square kilometres of the UK – an area roughly the size of Herefordshire – at risk of flooding during a storm surge. Even if “all worthwhile flood-defence schemes were to be built,” a spokeswoman for the CCC told me, “more people and properties [will be] exposed to high levels of flood risk by mid-century”.

Individuals and businesses are, increasingly, having to bear the cost. In some areas of Cumbria, after three major floods in a decade, insurance excesses now reach £25,000. The Association of British Insurers predicts that a major flooding event in London could have economic consequences comparable to the recession that followed the 2008 financial crisis.

For years the UK government has debated whether or not to replace the Trident nuclear programme. Its renewal will cost a minimum of £205bn. The most likely threat to the defence of the realm may not be a nuclear strike, however, but the waves that our deterrent lurks beneath. Following storms Desmond and Eva, the UK government pledged to spend a further £700m on flood defences, bringing the total to £3bn – 1/68th of the cost of Trident. Will it be enough?

Scientists – many of whom worked on the CCC report – have devised models to predict what is likely to happen when a storm of the magnitude of The Great Tide of 1953 hits us. Unlike the fault lines that menace Tokyo and the Californian coast, Britain’s pending catastrophe will not be caused by a single set of forces. Rather the threat comes from a complex set of conditions and possibilities: surge tides, fat seas, rivers swollen with rainwater, and debilitated infrastructure. The groundwork of these researchers and modellers, as well as the known weaknesses of our current infrastructure, produce a snapshot of a possible future. We cannot know for certain what will happen, but using this research, we can imagine the Great Tide of 2026.

Scotland will be first hit. A gale pushes the rising tide into the mouth of the Firth of Forth. Unhampered by any storm barrier – plans for which were rejected by the Scottish government in 2007, due to the impact it would have on shipping – the five-metre tide will batter the oil and gas facilities, food distribution depots and power station that line the estuary. The nearby petrochemical complex at Grangemouth, which handles 40% of UK oil supplies, will be flooded. Swaths of Scotland will be left without power, while broken bridges and choked roads leave much of the country without fuel. Food shortages will continue for months.

The Houses of Parliament, Westminster Abbey, the Tower of London, and 500,000 Greater London homes could all be flooded

In Yorkshire, as the storm moves south, homes as far as 10 miles inland will be flooded. Many people, unable to afford their insurance excesses, will be left homeless. As the tide continues its rampage south, in the Norfolk village of Happisburgh, those houses not already claimed by the sea over the previous decade will be demolished by waves. In the following months, residents of coastal towns, villages and cities up and down the country will probably head towards higher land. The housing market in coastal areas will collapse, while house prices further inland will continue to rise steeply.

As the Great Tide rounds on Essex and begins its rush toward the capital, Canvey Island’s fortified defences will this time hold strong. London, however, may prove less resolute. If the storm strikes after a period of heavy rain, which will have swollen tributaries in west London, the Thames Barrier will not be able to cope. The fatal conjunction of coastal, river and surface water flooding will break the Thames’ banks for the first time in 70 years.

If that happens, water will stream into hundreds of new houses built in Thurrock – which lies on London’s flood plains – to ease the housing crisis of the early 21st century. In keeping with a stark warning issued by the Environment Agency in 2012, many of the city’s best known monuments and institutions, including the Houses of Parliament, Whitehall, Canary Wharf, Westminster Abbey and the Tower of London, along with 500,000 Greater London homes, will be flooded.

More than 50 tube stations, including Waterloo, King’s Cross and London Bridge, will be filled with water. Major electricity grid sites around the capital will be taken offline, as the already strained healthcare system struggles to cope with the influx of the sick and injured. The following week, the London FTSE will collapse to new lows. Russian oligarchs will watch news footage of the water lapping at their property investments in dismay.

The threat to property will not solely come from the elements. As in 2015, when local police forces hired the services of private security guards to patrol the houses of those in Cumbria who had been displaced by floods, looting will become a major problem as the water finally retreats.

London As Venice by Robert Graves and Didier Madoc-Jones, aerial photograph by Jason Hawkes ©www.postcardsfromthefuture.com @futurepostcards. Photograph: Robert Graves and Didier Madoc-Jones

The 1953 flood inspired drastic action to avoid just such a scenario. A report led by Sir Hermann Bondi, professor of mathematics at King’s College, London claimed that another surge tide could fill the underground system with seawater, ruin telephone exchanges, disrupt gas and electric services and paralyse London for as long as six months. The cost of such damage stretched into billions – a bill that, as one government official said at the time, “would not count human misery and loss of life”. Today, the estimate has risen to an incomprehensible £200bn.

It was 17 years before a solution was settled upon by the Greater London Council. The idea was proposed by Charles Draper, an engineer from Rendel, Palmer & Tritton, one of scores of companies that, following the 1953 flood, hoped to find a solution to the question of how to keep London safe from a repeat attack. Every December, Draper would convert his garage in Horsham into an impromptu bar, and invite friends around for a celebration. One year, Draper was fiddling with a gas tap prior to one of these parties, when inspiration struck. He saw in the simple design of the tap, which swivels in its casing to open and close the air flow, a principle that could be scaled up, even to a size that could tame a river. Draper’s design – six gas-tap style gates under stainless steel shells that span the river in a phalanx – was chosen from many.

On 8 May 1984, not long after Draper’s death from cancer, the Queen officially opened the Thames Barrier. At the time of the barrier’s construction, it was estimated that it would provide London with protection from surge tide floods from the sea until 2030, but a study by the Environment Agency, published in 2009 claimed the barrier, if properly maintained, could in fact provide sufficient protection till 2070.

The estimates may have been correct – although there is some disagreement among experts – but unforeseen demands are being made on the Thames Barrier today. In 2013-14, it was closed no fewer than 50 times, the maximum recommended number of annual operations to avoid the risk of mechanical failure. Previously, the barrier had closed only 124 times in total since it began operating in 1982.

The steep rise in closures is because the barrier is now being used to manage flooding in ways for which it was not designed. Fewer than 10 of last year’s closures were a result of surge tides, such as the 1953 flood. The remainder were to deal with fluvial flooding, when an excess of rainwater causes a river to swell over its banks. To deal with this problem, the barrier closes at low tide. This creates a reservoir upstream into which rain-heavy tributaries pour and, finally, offload into the English Channel. “The barrier is there to protect London from a surge from the sea,” says Dick Tappin, an engineer who worked alongside Draper on the construction of the Thames Barrier. “It is not there to protect London from heavy rainwater.”

As the events of 1953 demonstrate, the consequences of a flood from the sea are far greater than the consequences of river flooding. Nevertheless, a combination of the two would test the system in unprecedented ways. “If London would receive the comparable amount of rainfall that caused floods in England in 2007, the consequences are expected to be much more significant,” says Dr Ana Mijic from the department of civil and environmental engineering at Imperial College London. Mijic believes there could be “in the tens of billions of pounds in property and infrastructure damage, and high probability of severe impact on human health and lives”.

Carlisle United’s football pitch after Storm Desmond in December 2015. Photograph: Oli Scarff/AFP/Getty Images

Lord Krebs, a gaunt man with a brush of thick grey hair, is accustomed to bucking expectations. His father, Hans Krebs, who won the Nobel prize in physiology a few months after the 1953 flood, expected his son to follow his example by going into the medical profession. Midway through Krebs’s interview to study medicine at Trinity College, Oxford, where his father was a fellow, he revealed that he wanted to study zoology instead.

In 2001, after a distinguished career as a lecturer in zoology at Oxford and abroad, Krebs, chairman of the newly formed Food Standards Agency, clashed with the government. He claimed that the authorities had not adequately understood the risks posed by the foot-and-mouth outbreak. Krebs was proven appallingly right – the epidemic would result in the slaughter of 10 million sheep and cattle. In 2003, Krebs caused further controversy when he stated that so-called organic food has no benefits compared with food grown on conventional farms.

In 2007, Krebs became an independent crossbench peer in the House of Lords. Now, as a chairman of the CCC, Krebs, who is also president of the British Science Association, is proving unpopular with government ministers across the political spectrum. “The government and the public don’t understand what exactly is meant by risk of flooding,” he told me when we met earlier this year. “We talk about a one-in-a-hundred-year risk of catastrophic flooding. But if a hundred places in the country carry that risk, the likelihood is that one of them will flood every year. It may not be you this year, but it will be someone, somewhere.”

Last winter’s floods have resulted in some action, Krebs concedes. The government has instigated two reviews, one looking at short-term measures to protect major cities from floods, and another taking a longer-term perspective, asking how we can manage water catchment, ensuring it disperses into rivers, dams and groundwater systems. It is crucial work. “Current defences are being overtopped with devastating effects,” he said.

Despite these efforts, Krebs believes that we are missing crucial opportunities to better prepare the country for the effects of climate change. For example, he believes that developers should retain some liability for flood damage when they build new homes in flood plains (where so many of the UK’s towns and cities are located). “Right now, a developer can build 20 houses and walk away, while the hapless person who buys the house must carry all of the cost when it’s flooded,” said Krebs.

Krebs also worries that because last winter’s floods occurred in the north, there may be less momentum to act than if they had hit the south-east. “There may be a south-centric view that, if these things happen in the north it’s less significant,” he said. “It’s often the case that it takes a crisis to create a change of mindset.” Until London ceases to be safe and dry, in other words, action may remain sluggish.

While Mori polls show that 70% of UK residents who live in areas of flooding are aware of the risk to their homes, an increasing number of people are unwilling to wait for disaster before they take action. Lincoln Miles, 22, runs the UK’s only survivalist store, Preppers Shop UK, in Bedford, which opened its doors in July 2014. “I think we are a few years away from a major social breakdown and not too far away from a major climate breakdown,” Miles told me recently. “We’re teetering on a social knife edge and at some point soon something is going to snap.”

Lincoln Miles at his survivalist store Preppers Shop UK in Bedfordshire. Photograph: Frantzesco Kangaris/The Guardian

Preppers stocks a wide range of supplies, many of which are intended to help a person survive in the event of extreme flooding. In some corners of the shop, it looks a bit like a DIY store, complete with shovels, saws, high-visibility jackets and inflatable dinghies. Elsewhere, it is closer to a post-apocalyptic bunker, with gas masks, crossbows, hunting knives and industrial-sized tins of beans. According to Miles, his customers, most of whom wish to remain anonymous, range from ex-military servicemen and bushcraft enthusiasts to lawyers, teachers and pilots. “Everyone can be a prepper, and preppers come from all walks of life,” he said. “We are currently growing at an exponential rate.”

Miles, whose style could be described as lumberjack chic – sumptuous beard, plaid shirt with the top three buttons undone, black bandana – became interested in the survivalist community in 2013, after reading an article about prepping in America. “I became obsessed with prepping,” he said. “I was constantly reading Facebook pages and forums.” As Miles began to assemble his own bug-out bag – a rucksack filled with basic items for survival such as water-purification tablets and first-aid kits – he grew frustrated that there was no one-stop shop for the items he needed. Later that month he launched Preppers UK online.

Prepping, an idea imported from America, has been viewed by many in the UK as the hobby of cranks and weirdos. But Miles, who claims to be “fully prepared” for a variety of disaster scenarios, is unmoved by the sceptics. “These days people are realising that the world is vulnerable,” he said. “The emergency services aren’t always there to protect us. People are increasingly taking the future into their own hands.”

In that respect at least, Lord Krebs shares Miles’s view. He believes that preparedness for disaster is not the sole responsibility of the state. “There are measures that can be taken to reduce vulnerability,” Krebs told me. Even if you’re not quite ready to order a bug-out bag, everyone, Krebs believes, should consider the water resistance of flooring materials. “Everyone,” he added, “could raise their electrics off the skirting board.”

While it is relatively easy for individuals to prepare for a week or two without electricity, buttressing national infrastructure against the threat of floods takes much longer and requires not only money, but political will. As the authors of a 2004 government report into flooding state: “If we want to alter land use in flood plains and alongside rivers within cities, it could take decades for changes in planning policies to take effect.” Knowing exactly when, where and how to spend money in order to prepare a country for drastic change requires input from scientists with a certain talent for predicting the future.

Professor Richard Betts, a Met Office Fellow and chair in climate impacts at the University of Exeter, is one such scientist. His predictions are relatively conservative. “Wheat yields may tend to increase in the north of the UK, possibly by up to 30%,” he says, of the effects upon the UK of a 2C rise in average global temperature, “while yields in the south may decline by the same amount”. Betts agrees that, in the long term, the “most significant and observable” effect of climate change on Britain will probably be coastal flooding. The value of housing under threat of inundation will drop, he says, while insurance premiums will rise.

The sweltering summer of 2003, when roads melted, train lines buckled, the London Eye closed and a record temperature of 38.5C was recorded in Brogdale in Kent, will become “a regular occurrence under a two-degree world,” he says. (The Met Office estimates that “summers as hot as 2003 could happen every other year by 2050, as a result of climate change due to human activities”.) Health services will need to adapt accordingly.

Krebs is less conservative in his estimations. He is, in fact, concerned that the disaster models do not go far enough. Even if fully implemented, he believes that the international agreements made in Paris last year to halt the global rise in temperature, will, in reality, only take us somewhere closer to a 3C rise by 2050. The higher the temperature rises, the greater the effect on the sea level. “We need to ask some difficult questions,” Krebs told me. “Most of the assumptions are based on a 2C rise in average global temperature. I think we should be looking at four.”

As seas surge, coasts retreat, and rain falls and falls, we have grown numb: 2C or 4C – who cares? It’s all catastrophic

Even as ice melts, seas surge, coastlines retreat, insurance premiums rise and the rain falls and falls and falls, we have grown numb to the dread statistics: 2C or 4C – who cares? It’s all catastrophic. Today, the baby-boomer’s vision of future skies busy with flying cars seems appallingly naive. Not because technology has fallen short of those optimistic expectations, but because many people do not envision a future of progress. Instead, the future we imagine is one of decline, or, at the least, perilous change.

There may, however, be hope. At 96 years old, James Lovelock is perhaps the best known of all apocalyptic scientists. His 2006 book, The Revenge of Gaia, states that we are in the midst of “a global decline into a chaotic world ruled by brutal warlords on a devastated earth”. Nevertheless, Lovelock remains sceptical about our ability to predict the future accurately. “I just don’t think that mathematical models are able to predict the future that well,” he said. “All sorts of things could happen. There could be a big volcano, something totally unexpected, that cools the whole darned lot off. It can happen.”

Then again, we may not be so lucky. “We live 70 yards from the sea,” Lovelock told me from his home on England’s south coast. “It’s rising but you wouldn’t notice it yet. And even if it rose by two or three metres, all it would do is take the road at the end of our garden away.” He paused. “Oh, and London and New York too, of course.”

Main photograph: Seaham harbour, County Durham in 2013. Credit: Owen Humphreys/PA

This article was amended on 7 July to make clear that Lord Krebs is just one of the chairmen involved with the Climate Change Committee. An earlier version of the piece also incorrectly referred to the “Forth of Firth”, rather than the Firth of Forth. We have removed a reference to Longannet coal power station that closed earlier this year.

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