There’s panic on the streets of London. Well, they used to be streets, but now they’re urban riverways submerged under 20ft of flood-water. They snake their way around trademark city environs. Trafalgar Square, Whitehall and Docklands, all drowned. There are bodies everywhere, floating face down — some of the 200,000 dead. Choppers buzz about overhead, and police boats roar past upper floors. Surviving Londoners are screaming from the rooftops. They need help, they need food, and they need to get out of this waterlogged hellhole.

The description above is not some environmental agency worst-case playbook. Nor is it the dire prediction of a government think-tank. It describes the mid-point climax of the new disaster movie Flood, during which a freak spring storm and a tidal surge suddenly combine to drown London in unstoppable water. It’s a bizarre testament to the environmental instability of our times that a movie once conceived as fantasy should have such eerie contemporary currency. “It’s frightening to set out to make a piece of science fiction and then see it become science prediction before your very eyes,” says the director of Flood , Tony Mitchell.

The movie, adapted from the 2002 airport novel by Richard Doyle, follows the intertwined personal fortunes of a rugged marine engineer, Rob Morrison (Robert Carlyle) and his estranged scientist father Leonard (Tom Courtenay). Rob, a consultant at the Thames Barrier, blames Leonard’s obsession with climate change and the flooding of London on the death of Rob’s mother. But when flooding becomes a reality and the barrier is breached, Rob ultimately realises his mistake and hopes to save both his relationship with his father and the city itself before the final reel (hey, I said it was an airport novel).

Nonetheless, so much in the movie will have resonance for British audiences. The visual tropes — the police speedboats, the residents on rooftops and abandoned water-logged vehicles — are straight out of Tewkesbury last month. As is the defensive language of the Deputy Prime Minister (David Suchet), who wants to know why his government scientists didn’t see this coming. Oddly, says Mitchell, the first reality-check for the production, which began shooting in budget-friendly South Africa in April 2005, was not English, but American.

“It was about six months into production when Hurricane Katrina hit New Orleans,” says the Canadian Mitchell, whose previous film was also an environmental disaster movie, called Supervolcano (about an eruption in Yellowstone Park).

“Once that happened anybody who didn’t quite understand the scenario of the movie, or thought that it was complete fiction, realised that it really could happen.” Mitchell adds that although he was making a piece of popcorn entertainment, the increasing prevalence of environmental disasters such as Katrina meant that he also felt a moral responsibility to address this issue surrounding his story with a certain sober detachment. “Naturally, I don’t ever want this film to become a reality,” he says. “But when you’re making it, you want to get the details right. You want to show how government ministers might make the wrong decisions, how timing is key and how, when dealing with natural forces, you are always, always, the underdog.”

Flood isn’t exactly your traditional disaster movie. That hysterical and cathartic genre began with science fiction B-movies such as When Worlds Collide (1951), and then climaxed in the 1970s with big budget epics such as Earthquake , The Poseidon Adventure and Meteor before finally resurfacing in the Nineties with effects-laden flicks such as Twister , Volcano and Dante’s Peak .

Those films were typically elemental tales of man against wild and irrational nature. Even though they depicted the best crowd-pleasing devastation that computer programes could render, the ingenuity and the resilience of humankind always won the day. Now, however, everything has changed. In films such as Flood and The Day After Tomorrow , nature is no longer the enemy but a victim of man’s base insensitivity and commercial greed. Here the devastation is double-edged and self-inflicted, while the urge to survive is cautionary and less triumphant.

Elsewhere populist movies such as Ice Age: The Meltdown , The Simpsons Movie and even Al Gore’s critically acclaimed documentary An Inconvenient Truth have reflected an increasing urgency within Hollywood to address environmental issues as directly as possible. This has even extended to off-camera activities. Here both the forthcoming Russell Crowe western 3:10 to Yuma and Paul Haggis’s Gulf war movie In the Valley of Elah recently set the green standard by detailing the fuel efficiency of their production vehicles and the bio-degradability of the products used during filming. Meanwhile, the TV hero Kiefer Sutherland, aka Jack Bauer, has announced that his hit series 24 will be turning its attention to global warming, both within the show’s storylines and in all other aspects of production.

But let’s not get carried away with ourselves, says Mitchell. Global warming can be a mood killer, and he doesn’t want prospective Flood audiences leaving the cinema in either a sombre depression or heady apocalyptic panic. “I don’t think that people who see the film will be quaking in their boots and worrying about their homes,” he says. “Really, there are huge amounts of protection in place for the film’s scenario not to happen.”

Steve East, a spkesman for the Environment Agency, agrees. “That level of flooding is actually impossible,” he says confidently. “If you put together the worst weather conditions that have ever been in the North Sea and the highest tide ever recorded, you still can’t come up with any scenario where the Thames Barrier’s defences are breached.” Sounds like a line from a movie, just before the big wave hits, doesn’t it? East adds, interestingly, that the Environment Agency is happy to support the film to get the “real” messages about flooding out there. Which are? “We need to start looking ahead, for flood risk management for the next 100 years.”

The appetite for disaster movies will be as big as ever, Mitchell predicts. He is currently seeking his next project, “possibly about bird flu”, he jokes. Disaster movies tap into something fundamental within the human condition, Mitchell adds. From weather-based stories to car crashes to global events such as 9/11, we are all hooked on observing the unthinkable.

“Horrendous, horrific things happen, and we as a species are just intrigued by it,” he says. “I suspect it’s because we have some in-built need to feel grateful for our own mortality, and our own survival. It’s hard to tell, and it’s weird, but I like making those movies.”

Flood is released on August 24

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