For at least 855 years, the village of Sipson has stood on Middlesex fields. By 2020, however, it will almost certainly have vanished, its 700 homes, shops, pubs and school flattened to make way for Heathrow's third runway. Patrick Barkham reports on a village living on borrowed time

Elm trees hugged the main street in Sipson when Jack Clark earned his weekly 3s 9d on Thomas Wild's farm. Fields, he recalls, were lined with hummocks of strawberries. Grapes and peaches grew in glasshouses. Plums dangled over the walls of orchards. There was a pump for spring water. A mile-and-a-half down the road was a small cluster of cottages called Heathrow. The only grey objects in the sky above the market gardens of Middlesex were Clark's pigeons.

Jack Clark is 94 and still keeps pigeons at the bottom of his cottage garden in Sipson. Around him, however, is a landscape utterly transformed. At night, he stands in his dressing gown and watches a line of eight aircraft, lights ablaze, hanging in the sky like Christmas lights as they make their descent into the world's busiest international airport. A field away, a satellite dish whirs round and round. The red lights of a control tower blink over the rooftops. Sipson, a village of 700 homes, is marooned between the M4, the M25 and Heathrow.

Where he would bird-nest as a boy, a boxy Holiday Inn now squats. Where he once played cricket on the street, people carriers stack up. And yet, against all logic, a small community survives in Sipson. You will see it if you look to your right seconds before touching down from your sunshine break in Barbados. Americans exclaim at it. There is a paddock of horses, the low beams of the King William IV pub, a primary school, a (converted) Baptist church, the post office and the butcher's, mock-Tudor houses, crescents of pale-bricked semis from the 70s. A village, a recognisable village.

This year, 855 years after the first surviving records of a settlement called Sibwineston, the people of Sipson expect to be wiped off the map. From Gordon Brown downwards, the government, supported by airlines and the aviation industry, says that Heathrow must have a third runway. At Stansted, plans for a second runway will swallow two small hamlets, but not since wartime has such a large village been threatened. Sipson's 700 homes, shops, pubs, small businesses and school will by buried under taxiways, terminals, concourses and car parks by 2020 if this year's government review of its 2003 aviation white paper approves R3, as the aviation industry calls it. And, as BAA, Heathrow's owners, acknowledge, it is not an either/or choice. A third runway at Heathrow will not halt the need to expand other airports. Our insatiable appetite for cheap foreign travel means that the struggle to save Sipson will mirror other battles across the country in years to come.

A sickly image recurs on the streets of Sipson. "I've lived here for more than 30 years and just rubbed along with the airport," says Christine Shilling, whose house is 200 yards from the proposed taxiway just outside Sipson. "Now I see it like a cancer, spreading across the landscape." Bryan Sobey stands in his front room next to three wistful oil paintings of trains. "Heathrow used to be what I called a 'friendly-advantage' place. It supplied work. It was a bit of a family, in a way. It is now a cancer just about to become malignant." He and his wife Ann bought their house in 1959. Coming from Devon, they had seen entire villages sacrificed for military camps during the second world war. "But this is so that someone can go to Malaga," says Sobey.

Heathrow was born in the war. A small aerodrome with a grass runway was built by Fairey Aviation to test aircraft in 1929. According to local historian Philip Sherwood - like every resident, drawn into the campaign to save Sipson - the air ministry knew that an airport so near west London would never be approved under normal planning laws. The second world war intervened, Fairey was evicted and Heathrow became a military airfield. "It was a ruse," says Sherwood. "They didn't start work on building the airport until May '44. Within a year, the war was over." The people of Sipson have a motto for Heathrow: "Deception since its inception."

This year, Sipson celebrates an inauspicious anniversary: 60 years of having been earmarked for destruction. Plans from 1946 show five runways and no Sipson, but money ran out. Heathrow remained a bucolic collection of marquees. "They had only just pulled down the tents when I arrived. The terminals were Nissen huts," says Sobey. In his early days as a customs officer intercepting smuggled diamonds, all the "bucket and spade" flights departed from other (now defunct) small airports nearby. He never imagined Heathrow's remorseless expansion. When Terminal 4 arrived in 1978, residents were assured there would never be a 5, 6 or 7. But by the early 1990s, with T5 on the statute book, a third runway was mooted to serve Terminals 6 and 7. Rejected in 1995, the plans for R3 were quietly resuscitated at the century's end.

Three developments make 2006 a potentially fatal year for Sipson. Buried in the chancellor's pre-budget report in November last year was an announcement of "extensive" research on pollution problems at Heathrow "aimed at identifying solutions that would allow construction of a third runway to take place within relevant air quality limits". Then there is the government's own review of Britain's transport infrastructure by Rod Eddington, the former British Airways chief executive. It is widely expected to streamline the planning process for major infrastructure, making it harder for Sipson to block the runway. Finally, at the end of the year, the government will review its 2003 white paper. It had said Heathrow's expansion would be delayed because of noise and pollution problems. Lobby groups are now pushing for a positive decision on R3; the chancellor's activity suggests they will get it.

Sobey, the diligent president of Sipson's residents' association, knows every publicly available fact of the plans - and every detail he claims has been left out (such as how the roads will cope with the extra traffic from Heathrow's expansion). A calm, rational man, he struggles to comprehend the destruction of his village. "This is the total eviction of an entire community - their recreation grounds, country walks, schools, houses, small businesses. It's ethnic cleansing without the guns."

"Maybe it's primeval," says Shilling, who, with two other local women, helped set up Sipson's campaigning arm, the No Third Runway Action Group (NoTRAG). "Maybe it's biology. You fight for the nest. [But] it isn't just home. It's the school where generations of children have been educated. It's the wiping out of memories. It hit me as immoral, evil and unjust."

Anti-airport protests remain rooted in parochial concerns. But the people of Sipson know it is not enough to be Nimbys. "In the past, one group would say, 'Why not build the runway at Stansted where there's all those empty fields?' and the other would say, 'Why not build another runway at Heathrow, it's ruined already'," says John Stewart of the west London campaign group Hacan ClearSkies. "Now, it's more united."

Sipson's radicals tilt at the whole edifice of air travel, where predictions (UK passenger journies to increase from 200 million to 500 million a year by 2030) become targets. "I'm a caravaner," says NoTRAG's chair, Geraldine Nicholson. "I last flew five years ago. I'm not asking people to fly less. I'm asking them to pay the proper cost." It is ironic, says Sherwood. "Food is being imported from all over the world. Parsnips come from Australia to Heathrow. Before the airport, parsnips grew at Heathrow."

NoTRAG includes residents from Harmondsworth and Harlington, the villages to the west and east that expect to be similarly blighted beyond habitation by R3. Nearly 1,000 local people attended its AGM last year. Now Sipson hopes to mobilise the good folk of Richmond, Kensington and others across south-west London, who, they say, do not realise the increase in noise and pollution they could experience. They have written letters to ministers and, aided by green groups and road protest veterans, pledge non-violent direct action if and when building work begins. "It's a housewives' army," says Nicholson, 36. "Our strategy is to make the MPs listen but [transport secretary] Alistair Darling won't even visit or meet us."

Heathrow dwarfs Sipson. Each year, 67 million people rely on its 166 aircraft stands, four terminals (five from 2008) and two runways for work and pleasure, escape and return. There are 70,000 people who depend on the airport for their jobs and at least 100,000 more across the UK who are indirectly linked to Heathrow. Airlines also depend on it: in 2003, 83% of BA's passengers flew there.

But without expansion it is the airport, not Sipson, that faces extinction, argues Lord Soley, a resident of west London and former Labour MP who fronts the pro-expansion pressure group Future Heathrow. He hopes that the government will approve R3 by December. The airport is currently squeezed on to 1,227 hectares, compared with 3,100 at Charles de Gaulle outside Paris. Its flights are capped at 480,000 each year. If Heathrow cannot grow, he argues, it will die.

The inexorable upward curve of passenger numbers gives people a false sense of security, says Soley. It is like London's docks: in the 60s, record import figures disguised their relative decline; by 1980, it was all over and east London was ruined. Without a third runway, he says, west London faces the same prospect. Heathrow already serves fewer regional destinations than it used to; Frankfurt, Paris and Amsterdam serve more. Amsterdam is positioning itself as London's third airport: it flies to 21 British cities compared with Heathrow's nine, and fewer regional connections mean the loss of international flights. Book a flight from Edinburgh to Asia, for instance: chances are, you will be routed through Amsterdam's Schiphol airport.

"Heathrow is living on borrowed time," says Soley. "If it doesn't expand, it cannot survive." The third - short - runway would provide regional connections and preserve Heathrow's status as a European hub. "We need to address this argument in the context of north-west Europe," he says. The consequences of not expanding for the west London region are "too awful to contemplate". The government estimates R3 would generate more than £6bn in direct net economic benefits.

These economic arguments are played out in Sipson. Some feel forced to choose between their home and their job. One resident attends every anti-expansion demo but, with retirement two years away, is petrified that his opposition will get him the sack. Another local, a father of two who works for BA, is happy to talk but later calls to ask to remain anonymous because he fears speaking out will get him the sack. "I like my job. Mine is not an argument with BA. It is entitled to support the runway and I'm entitled to support my home. It's a fight between me and my employer's landlord. It's BAA's attitude to normal hard-working families that gets me."

"There are some things we can compensate for - house prices - and some we cannot - the sense of community," admits a BAA spokeswoman. Lord Soley argues that compensation must be fair and generous. BAA says it is. The BA worker desperately wants to move to give his family more space but says that he cannot because Sipson's depressed prices will not fetch him a comparable home near work. BAA has offered him and other residents affected by R3 a transferable bond which guarantees them or any future owner of their house the market value of their home as it stood in 2002, before news of the latest plans came out and caused a house-price slump. But residents argue that the third runway was first publicised in the early 90s, so their homes were blighted since before 2002. With normal life suspended as they await a verdict on the runway, villagers say it is virtually impossible to sell, even with the promise of a transferable bond. "It's a question of morality," says one. "How can you treat families like that? How can the government in the so-called fairest country in the world do this to working-class people?"

Publicly, BAA remains cautious over R3, which it says must be decided by the government. "Our position reflects the conclusion of the government's white paper, which is that an additional runway is desirable, but not at any cost," says a spokeswoman. "We know there are very challenging targets in relation to air quality and that this issue must be addressed before any possible runway can be considered." Even if extra runways are built at Heathrow, Gatwick and Stansted by 2030, she says, they will not meet predicted demand.

Sipson is stuck in a physical and emotional no-man's-land. If they lose, on the earliest reckoning residents would be forced from their homes before construction work began in earnest around 2015. The dispiriting dance of consultation-protest, consultation-protest might prolong the life of Sipson, but the community would die long before then. Rumours of R3 already swirl in a vicious circle: disillusioned residents move out and let their homes rather than sell them cheap. Renting newcomers - who are described as "the dregs" by one long-term local - aren't so bothered about Sipson's fate. Residents feel pushed out by BAA. "The more dead they make this village, the less arguments they will have," says Gerald Storr, the butcher. "We're like mushrooms," says Lynn Davis, who has lived in Sipson for 50 of her 57 years. "Kept in the dark and fed on you-know-what."

Quality of life is flagging. Noise pollution is surprisingly light because planes land parallel to Sipson, not over it. The air, however, is not fresh. Vapour trails scribble across the sky, converging into man-made clouds that blur the sun. "It's the creation of a post-industrial hell," says Shilling. Clark tends his potatoes and beetroot. "If it's damp, you get an oily dew on everything. If you grow cabbages or cauliflowers, you can't eat them because of the pollution." Sobey has a diffusion tube on his drainpipe. It reads 38 micrograms of nitrogen dioxide per cubic metre; the EU safety maximum is 40. The Sipson sceptics believe Gordon Brown's talk of "identifying solutions" to Heathrow's air pollution problem is code for massaging the figures downwards.

How does Sipson feel? "These are traumatised communities," says Shilling. "There are people who feel helpless and despairing. Others feel anger - all the classic bereavement reactions." Sobey is 76. He has been campaigning against Heathrow's expansion since he retired in 1989. How will he feel if he loses? "Ulcerous. I would feel leaden. Well, I do now. I haven't done anything I wanted to do when I retired."

In years to come, Nicholson's three sons will probably be the last generation to have any recollection of Sipson. Where Jack Clark once walked through lanes at dusk, Nicholson takes her boys to the ponds around BA's headquarters. Zach, 6, points excitedly at passing aircraft. "I tried to explain to him what would happen when the runway came. 'So we can't feed the ducks mummy?' he said. I said, 'But you like aeroplanes,' and he said, 'No mummy, I like the swans and the ducks.'"

Heathrow's R3 may simply represent the unfeeling sweep of market forces. Land use is constantly changing. When Jack Clark was young, Thomas Wild decided three crops each year would make more money than one. The strawberry fields were ripped up and lettuce and spring onions planted instead. "Old man Wild lived opposite the King William pub," remembers Clark. "He'd stand at his gateway on a Sunday. The boys would walk down Harmondsworth Lane and slide in the pub's back door so he didn't see them. The Wilds used to run the village. BAA is running it now."

He sits in his living room with the radiator turned up high. "If my old guv'nor came to life, he'd have 40 fits when he saw what they're doing to the village. I thought the third runway would not be in my time, but my doctor said I'll live to 100, so maybe I'll see it. Then I'll be buried under the concrete".