Farming in the British Isles is on the verge of a dramatic step towards industrialisation with the establishment of "mega-farms" for salmon, pigs and cows, which opponents claim put the environment and human health at risk. The Government signalled its backing yesterday for large-scale farms ahead of an announcement this week of a timetable for plans for a 25,000-capacity pig farm in Derbyshire. A decision on a planned 1,000-cow dairy unit in Wales is also imminent.

Pressure to meet growing demand for protein by radically increasing the size of farms has also spread to Ireland, where the authorities are backing plans to build one of the biggest salmon farms in the world in Galway Bay, doubling Irish salmon production at a stroke.

Farmers and officials insist the introduction of modern facilities offers a solution to Britain's voracious appetite for cheap meat by increasing production while maintaining or improving animal welfare standards and without affecting the environment.

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A spokeswoman for the Department for Environment, Food and Rural Affairs said: "Increasing the efficiency of food production will help us meet rising demand for food. This can be done on any scale and in ways that actually deliver environmental benefits. Large-scale farms are required to meet the same environmental and animal welfare standards as all UK farms."

But campaigners claim approval of the schemes would cause a rush towards factory farms across the country, imperilling countryside and coastline in a dash for cheaper food. Lord Melchett, the Soil Association's director of policy, said: "The solution is not to create huge-scale intensive operations that threaten our landscape, farming and rural communities. Large-scale industrial farms may be able to produce food a little more cheaply in the short term, mostly through reducing the number and cost of people employed. But we will end up paying a high price for what may be marginally cheaper food."

In the Derbyshire village of Foston, opponents claim plans for a vast indoor pig farm represent a dramatic leap towards techniques already employed in other parts of Europe and the US, where 100,000-capacity pig farms are common. A petition against the farm has collected more than 25,000 signatures including the actors Sir Roger Moore and Dominic West as well as the TV chef Hugh Fearnley-Whittingstall. Sir Roger has described large-scale farms as "concentration camps for animals". Opponents claim such farms will create enormous animal welfare problems where disease could spread quickly and the environment will struggle to cope with the slurry.

Midland Pig Producers, the company behind the Foston proposal, says it has worked exhaustively to ensure it meets all the concerns with state-of-the-art air scrubbing equipment to remove odour and an anaerobic digester to turn slurry into methane to power the farm. It claims it will also pioneer improved welfare conditions by using new "freedom farrowing crates" allowing sows and piglets greater movement. "We believe farms in the UK will have to get more efficient if the consumer's demand for British meat at a reasonable price is to be met," the firm says.

The National Pig Association denies Foston represents the industrialisation of pig farming. It will, they argue, offer the chance of increasing UK pork production as well as establishing higher welfare standards than European or US competitors. "Big does not necessarily mean bad in pig farming. Foston will apply technology and techniques that ensure better animal welfare and environmental standards," a spokesman said.

In Wales, the Government is expected to receive an inspectors' report at the end of May on whether a Powys dairy farmer can proceed with plans to build a 1,000-cow unit. Fraser Jones wants to triple the capacity of his farm near Welshpool. His opponents insist the scheme's approval will open the way for similar farms across the UK. Carol Lever of the World Society for the Protection of Animals said: "The importance of this decision should not be underestimated. If we allow this industrial dairy to go ahead, it could potentially change farming and the countryside for ever." Mr Jones defends the plan, saying: "We have gone to great lengths to address people's concerns. The cows, which would be inside for 250 days a year, would be continually monitored and the dairy would promote good animal welfare."

Similar arguments are being rehearsed about plans for offshore mega-farms. Environmentalists warn that BIM's proposals to build a fish farm off Ireland's Aran islands, capable of producing six million organic fish a year, risks playing havoc with the ecosystem by introducing a "huge quantity of biomass" into Atlantic waters. If approved, the scheme will be five times larger than any existing salmon farm off the British Isles.

Campaigners fear it will devastate wild salmon and trout stocks by introducing parasites and polluting waters with waste from the fish. Ken Whelan, professor of biology and environment at University College Dublin, described it as a "giant experiment". "The concern is it is moving very fast from a greenfield site to something bigger than Ireland's current national production. If people are truly interested in being sustainable, you have do it on a staged basis to be certain of the impacts." BIM did not respond to requests for comment. Previously, it said its proposals amounted to safe, efficient and sustainable fish farming.

Scottish producers insisted yesterday there are no plans for similar deepwater offshore farms in Britain but The Independent on Sunday understands that at least one major international aquaculture company is undertaking site feasibility studies in Scotland. An industry source said: "There is a strong desire to explore the feasibility of offshore farms where scales of production could be increased. The Irish situation is being watched closely."

Too close for comfort

Residents in Foston, Derbyshire, fear their health will be at risk if plans by Midland Pig Producers (MPP) are approved. The "mega-farm" will exacerbate conditions for those who live in Foston, who say it is already home to a women's prison, a Traveller site and an intensive poultry farm.

Sue Weston, 48, and her husband Steve, 50, believe their house, valued at nearly £500,000 six years ago and which overlooks the 70-acre MPP site, may now be impossible to sell. "It's going to be practically in our living room. We had the estate agent back and asked him what would happen if it's built. He said: 'You might not get £200,000 for it. I dare say you will never sell it.'"

Their son Tom, 19, had open-heart surgery two years ago. Mrs Weston believes the farm will be a threat to his life. "I don't feel that I can live here and put Tom's health at risk. Infections could be fatal to him."

Audrey Connors and Michael Connors put their house up for sale, but did not get any viewings. Mrs Connors said: "We just gave up. Who wants to buy a house with that monstrosity in front of it?"

Heather Saul