From a distance, the landscape looks like a tranquil slice of rural England. Pudding-shaped hills, green valleys rimmed with autumn-coloured trees. But there is something odd. Maybe half a mile away there is a brilliant white stripe against the slate-grey sky. One moment it is a thin spiral, like a tornado. Then it sinks down, only to billow again like smoke from a volcano.

Coming closer, it is possible to see that the cloud is composed of tiny whirling specks. Closer still, and we see that those specks are not tiny at all. Herring gulls are huge birds, each one a kilo in weight with a wingspan of 4 1/2ft. A thousand of them in the air together are a tonne of hardened muscle wielding a terrifying armoury of beak and claw. And there are many more here than a thousand. Exponentially more. We are heading into a zone where gulls not only outnumber their human neighbours, but outweigh them. Gull city.

The city of the future. The way things are heading, Britain’s town centres are going to be overrun by an army of voracious and aggressive birds that will hold the rooftops against all-comers. They have already made headlines with their attacks on humans, whose heads they slash, raking them with their claws at 40mph, and they are notorious for the sleep-defying intensity of their cries, the corrosive damage caused to buildings and cars by their droppings, and their cargoes of disease.

What began as a nuisance is becoming a pestilence. Fifty breeding pairs in a town are all it takes to make a deleterious impact, and many already are way beyond that. As long ago as 2004, Swindon had 87 pairs, Cheltenham 151, Worcester 342, Bath 536, Newport 800, Bristol 1,933, Gloucester 1,996 and Cardiff 3,103.

In traditional coastal communities, where eggs and young are open to predation and the adults struggle to find food in a degraded sea, the breeding rate per pair is as low as 0.07 fledged young per year — an average of one every 14 years. In towns, where there are no predators and the gutters run with food, the birds breed earlier and routinely produce two or three chicks a year. Combined with their longer life expectancy — 20-plus years is normal —- it means populations are rocketing by 25% annually. Aberdeen, Cardiff and Gloucester are all strong candidates for the first 5,000-pair colony. Five thousand pairs means not only 10,000 adult birds yelling, defecating and racing for food, but also between 10,000 and 15,000 permanently hungry offspring and 4,500 immature non-breeders — a grand total of nearly 30,000 gulls. You don’t need to be a student of Hitchcock to recognise the potential for violent conflict.

Urban nesting by gulls in Britain is a new phenomenon. Before the second world war it was unknown, but at the current rate Britain will have more than a million breeding pairs by 2014. Two species are on the march: the herring gull, Larus argentatus, and the lesser black-backed gull, L. fuscus. They are of similar size and both need to eat 15% of their body weight daily. In urban Britain this is as easy as breathing. Gull city is gull heaven.

Approaching the white tornado, I soon see why. My companion, Peter Rock, can reasonably claim to know more about urban-nesting gulls than any man alive. After a few hours in his company, I can reasonably claim to know more about urban-nesting gulls than any man alive except Peter Rock. He seems an unlikely champion in the battle of man against bird. With spiky grey hair and beard, jazzy grey jacket and jeans, he looks more like an art teacher than your average birdie anorak.This is no accident. Until 2002, when he became Britain’s first full-time professional urban gull-watcher, art teacher is exactly what he was. Before that, since 1979, he had been observing and ringing gulls as an increasingly obsessive hobby, telling anyone who would listen that we faced a massive challenge for control of our rooftops. At first he watched urban gulls “simply because they were there”, but soon realised he was venturing where no researcher had gone before. “By default,” he says, “I became the national expert.” He has ringed more than 6,000 locally born chicks and tracked them throughout the length of Europe and deep into Africa.

We are a few miles from Bristol, heading down a lane of thickening mud. Abandoning the car, we splash along a deeply puddled track, over a fence and up a steep bank of sticky red clay. A few boulders are strewn about; some weathered fragments of an old brick wall; an ankle-high leaf-storm of litter clinging to the nettles. On bags and packages beneath our feet is a roll call of the retail and fast-food aristocracies — Tesco, McDonald’s, KFC…

What we see from the crest is two enormous craters — old clay pits big enough to swallow entire villages, but swallowing instead household garbage from towns across southwest Britain. In 10 years it will collect a literally unimaginable 2m cubic tonnes. As we watch, a 12-wheeler waste truck loses its grip in the mire and has to be dragged up Trash Mountain by a bulldozer. Once disgorged, its load is pressed down by a heavy yellow vehicle with spiked wheels, like some medieval war machine. The whole scene is viewed subliminally through a blizzard of wings, the air solid with birds. For them, the compacter is a food processor, breaking the stuff into peck-sized pieces, an endlessly rolling buffet that never runs out.

Rock calculates a total of 3,000 gulls. They come and go throughout the day, so that this first lunch-time sitting will be replaced by another, then another and another. The same thing is happening at landfills across the country. A national franchise of gull heavens. Rock plants a tripod and lines up his telescope. “His” birds stand out in the crowd like punks at a wedding. Ringed as nestlings, they wear brightly coloured sleeves on their legs, engraved with letters and numbers legible through a telescope at 300 metres. The colour combinations — blue, red, yellow, orange, green, white, black — tell him the age of the bird. The coding identifies the individual. His notes tell him when and where he last saw it. First up is a nine-year-old herring gull that he sees here regularly. Then a lesser black-backed of the same age not seen since July; an eight-year-old herring gull not seen since May; a seven-year-old absent since January… All have one thing in common. Like hundreds of thousands of others across the country, they seldom feel the ruffle of a sea breeze. Every last one of them was born in town, where their high intelligence and ruthless aggression are now causing panic. If the first prerequisite of a successful campaign is to know your enemy, then urban Britain is in for a tough fight.

Gull heaven’s principal architect was the Clean Air Act of 1956, which meant that refuse had to be dumped rather than burnt. Add to this the escalating garbage bonanza of throwaway consumerism, and you have the longest dinner invitation in history. Towns have other attractions too. Rooftops are warmer than cliffs (ambient temperatures are between 2C and 6C higher than in open country); street lighting allows round-the-clock feeding, and the next meal is never far away. Even on farmland, it might take a bird six to eight hours to eat its fill. At a landfill it can be replete in 20 minutes.

Textbooks will have to be rewritten. By nature, the lesser black-backed gull is a migratory species that spends its winters around the coasts of Iberia and north Africa. But given the warmth and ease of urban living, fewer and fewer are making the trip. By Peter Rock’s calculation, more than a third now live here permanently. As this confers a significant breeding advantage — they get the pick of the nesting sites — Darwinian theory says the residents will become the dominant strain and so the pressure on towns will increase exponentially.

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