Villagers prepare to defend their picturesque heritage against claims of wildlife and the sea

The prospect of invasion has occupied the minds of those living on the southern fringes of England for centuries, although the threat from Napoleon has long since receded and a scattering of pillboxes on the hillside is the only hint of the cross-Channel menace once posed by Hitler.

But in the beautiful Cuckmere valley, Sussex, they are preparing to take on their most implacable foe. The scene is set for the biggest challenge: The People versus The Sea.

At stake is one of the most picturesque settings in the country, known across the world through films, photographs and tablemats. At one end lies the English Channel and the shimmering white cliffs of the Seven Sisters; inland are meandering waters and grazing lands that have existed for more than 150 years.

But the Environment Agency wants to let the sea take control, flood the area and make a wildlife haven for birds. Some of the locals and visitors - about 1,000 of them have signed a petition so far - are less than impressed by the prospect.

Stefano Diella, the landlord at the Golden Galleon pub, believes returning the valley to its natural state might be popular with the binocular brigade but won't attract mainstream tourists. "What we have in Cuckmere Valley is the Colosseum. We don't want an obelisk just because it's environmentally friendly."

The problem stems from the industrial vigour of the Victorians. In the 1840s, they decided that the Cuckmere river was too bendy on its way to the sea and built a straight-line canal to cut the time coal barges took to reach inland areas. It also gave shore-based military a quick route back to their defensive garrison in the event of a foreign incursion.

Now, after decades of water slapping against the sides of the man-made channel, the wooden barriers protecting the waterway are, according to the Environment Agency, crumbling. Replacement with concrete and steel would cost £2m. The agency argues that, with global warming raising the sea level by 6mm a year along the coastline, the best option is to breach one side of the waterway and allow the sea to take control.

The effect would be to make 113 acres of salt marsh and mudflats, providing a haven for wading birds. Eventually, the agency wants to link the waters of the meanders - the winding, silted-up remains of the river's original course - with the sea's ebbing and flowing tides.

For Nigel Newton, the American chairman of Bloomsbury publishing who owns one of the three former coastguard cottages perched precariously on the cliff top, such action would turn the view from his back window, of the meandering waters of an English seaside valley, into one reminiscent of a "First World War battlefield".

The project would be devastating for the look of the area, which has been featured in countless films, including Brighton Rock and Robin Hood, Prince of Thieves, he claims. Second World War aircraft frequently buzz over the brilliant white cliffs, which provide a more shimmering backdrop than those down the coast at Dover.

Mr Newton has secured the services of Alan Edgar, a town planner, to counter the proposals in a dispute that has divided the area, which depends heavily on the 450,000 visitors a year to fuel its economy.

Many fear that those visitors will disappear if the paths by the curling waters of the meanders are replaced by a new path higher up the valley. They have experienced what can happen when visitors stay away: when foot-and-mouth in effect sealed off the areas, the pub - on the banks of the Victorian waterway - lost £150,000 and Mr Diella had to mortgage his mother's house to pay his staff.

Mr Edgar also claims that if control of the area is relinquished to the power of the sea, the first of the cottages will crumble into the waters within 10 years. The rest, he predicts, will follow soon afterwards.

"This is the most famous place in Sussex. The signature of Sussex. They are fiddling with it," he says.

Opponents of the scheme are calling for a public inquiry. The Environment Agency has already relented once and said last week that it would apply for planning permission for the project in a proposed South Downs National Park.

Yet the agency remains committed to the project, and contested the fears of some of the locals. It hopes to start work next year. If it did not, it warned, the sea would soon flood the area anyway.

Robert Beasley, of the Environment Agency, said: "It will be a big boon to tourism in the area. It will transform what in environmental terms is a sterile pasture into a complete haven for birdlife." The cottages had little hope in the long term, he said. "The sea is coming."

Despite the petition at the pub, some of the visitors basking in the sun yesterday supported the Environment Agency. Among them was Tamsin Watt, a PhD student from Sussex University, working on a project examining beaches at risk from the threat of global warming. "That's the problem along the coast; you are trying to interfere with the natural process and power of the waves," she said.

"This would allow the coast to find its own natural balance. More wetland environments for this sort of area would be great."