It’s the August bank holiday in 2050 and the UK is sweltering under the worst heatwave on record. Temperatures across much of England have topped 40C for eight days running: they peaked at 46C, and remain above 30C in cities and large towns at night. The country’s poorly insulated homes feel like furnaces, and thousands of people have resorted to camping out at night in the streets and local parks in a desperate attempt to find sleep. Hospital A&Es are overwhelmed and wards are flooded with patients, mostly old and vulnerable people who have succumbed to dehydration and heatstroke. Already, the death toll is estimated at more than 80,000.

No, this isn’t the beginning of a dystopian drama, but a snapshot of a mid-century heatwave unless we prepare for the increasingly extreme weather that will be driven by climate breakdown. To say that the government has no credible plan for this, as the UK Climate Change Committee did last week, is – if anything – an understatement. Britain is woefully underprepared for extreme weather, and in a number of key areas we are going backwards. About one in 15 of England’s most important flood defences were in a poor or very poor condition in 2022, up from roughly one in 25 just four years previously. The government’s Great British insulation scheme is operating at such a slow pace that it would take nearly 200 years to upgrade the country’s housing stock, while Labour has rowed back on its ambitious plans to insulate 19m homes within a decade.

It seems that neither of the major parties are especially bothered by the meteorological mayhem that awaits us. Extreme weather, especially heatwaves and floods, is set to be all-pervasive and will have a colossal impact on our lives and livelihoods. A recent report by the European Environment Agency warned that climate breakdown would bring “catastrophic” consequences for an unprepared Europe, most notably through heat stress, river flooding and flash floods. And this applies equally to the UK. Disruption to transport and utilities, interference with industrial and business operations, serious pressures on food production and supply, and increased burdens on the health service and hospitals, will conspire to make day-to-day living harder and far more unpredictable.

Heat is the foremost menace. In July 2022, temperatures in parts of the UK topped 40C for the first time ever, contributing to more than 4,500 heat-related deaths that year. The longer, more frequent and more intense heatwaves forecast for the middle of this century could add another zero to this figure. We can’t easily predict future peak summer temperatures, but they will increasingly break the 40C mark. The mock-up Met Office forecast for 23 July 2050 was almost matched by the reality of 19 July 2022, which was the UK’s hottest day on record. For future temperatures, the sky’s the limit.

Extreme heat isn’t the only problem. We are already more likely to have our homes flooded than burgled, and as episodes of intense rainfall ramp up, the number of homes affected by flooding – which is now one in six in England – will grow significantly. “Atmospheric rivers” – ribbons of moist air that are typically about 2,000km long – will become more common as the planet continues to heat up. These will play a big part in flooding, bringing days of extreme rainfall without respite, saturating the ground and filling river systems to bursting.

Meanwhile, longer and hotter heatwaves will lead to more “supercell” thunderstorms. Today, these prodigious convective storms are more common in the US interior than in the UK, where they whip up tornadoes and destructive hailstorms. Last December, a supercell storm hatched a tornado that damaged properties across Greater Manchester, providing an early warning of what lies in store. Torrential rains associated with supercell storms are one of the main drivers of flash flooding. In towns and cities especially, where concrete and tarmac prevent infiltration, flood water can build up with astonishing speed, overwhelming drainage systems, bringing transport to a standstill, and pouring into basement flats.

And the threats don’t end there. Alongside saturating floods in winter and summer, and more powerful and frequent wind storms, rapidly developing flash droughts caused by a combination of very low rainfall and humidity levels will bring massive challenges for agriculture. A 2022 report predicted that crop yield failures in the world’s “breadbaskets”, such as Canada, the US and China, will be 25 times greater by 2050 than they are today. Extreme weather will ensure that failed harvests become increasingly common in the UK, too. When you also consider the growing threat of serious wildfires, and increased coastal flooding due to storm surges pumped up by rising sea levels, the overall picture becomes pretty grim.

So, is there anything we can do? Climate breakdown will affect every one of us. We can, however, seek to mitigate its worst impacts. But we need to do more than just tinker. Preparing Britain for the onslaught of extreme weather that is coming will require us to completely reboot our climate mitigation plans across towns, cities and the countryside.

Much of our flood response comes down to land use. Rehabilitating peatlands and reforesting uplands can soak up colossal volumes of water, while setting aside low-lying land for river overspill can reduce the threat of floods farther downstream. To help people cope with extreme temperatures, we need to green our towns and cities. This means more green spaces and fewer car parks, alongside major tree planting to provide cool and shade. We should be replacing tarmac and concrete with more permeable materials to help reduce the impact of flash floods. Painting buildings white and using reflective materials on roofs can reduce the temperatures of urban areas by several degrees.

We also need effective warning and rapid response systems to limit the threat to life from flash flooding and wildfires. But above all else, and to prevent heat deaths on a massive scale, we need to insulate, insulate, insulate.

• Bill McGuire is professor emeritus of geophysical and climate hazards at UCL, and the author of Hothouse Earth: an Inhabitant’s Guide