In what will be a landmark human rights case in the UK, the farmers allege that the pipeline destroyed their land and forced them into destitution.

A British law firm representing the farmers has written to BP, accusing the company of benefiting from harassment and intimidation meted out by Colombian paramilitaries employed by the government to guard the pipeline.

BP insists that it has acted responsibly and that landowners were fairly compensated during the construction of the pipeline.

However, the farmers say that those who tried to stop the development were either forced by the paramilitaries to leave their homes or were murdered.

Local lawyers brave enough to take their cases to the regional ombudsman also faced intimidation and abuse. William Garcia Cartagena, a local attorney, was murdered while preparing a compensation case against a consortium of oil companies including BP and the Colombian authorities. Mr Cartagena's successor, Marta Hinestroza, fled Colombia for Britain when she discovered that her name was on a paramilitary hitlist. In November 2002 the Home Office granted Ms Hinestroza political asylum after she told of the threats she faced while working in the region.

Today, a team of lawyers from the leading firm of human rights and personal injury specialists Leigh Day & Co is flying home after taking statements from 60 farmers who say their lives have been ruined. Some of these allegations include incidents of rape and sexual harassment.

Martyn Day, the Leigh Day partner leading the case, says he is aware of the dangers he and his team face. "But what should we do," he asks, "leave these people without any legal help at all? We have been massively moved by hearing the stories of the farmers. It is clear this group of once respected and well-off members of the local community have been forced on to the scrap heap and are now living among the most deprived people of Colombia," Mr Day said.

"It's terribly depressing that BP holds itself out as a leading force for social and corporate responsibility but when it comes down to it they have been prepared to see lives destroyed so that they can increase their profits."

The farmers accuse BP of paying just a few hundred pounds for their land, which now supports the pipeline, and then failing to honour promises to compensate them for any damage caused by the construction.

Most of the farmers are illiterate and would have been unable to read the contracts they signed. In some of the statements they say that they were told that the pipeline would be built with or without their agreement.

Mr Day says that BP Exploration was the driving force behind the consortium that owns the Ocensa pipeline, which runs from the Cusiana-Cupiagua oilfields in the region of Casanare to the port of Covenas.

As soon as the construction work began, the farmers say they noticed an impact on the local water table. On some farms, natural springs that local people had relied on for hundreds of years began to dry up, while other farmers complained of flooding. Soon crops failed, fishponds became unsustainable and livestock perished in the fields. In the past 10 years Colombia's oil pipelines have become targets for insurgent groups. To stem the tide of attacks government-aligned paramilitaries have been deployed in greater numbers in camps based close to the pipelines. The soldiers have killed livestock for food and, when the farmers objected, threatened them with violence or false accusations of helping the guerrillas, Mr Day said.

"We are not contending that BP had direct involvement in any of these incidents. However, what we are saying is that in entering into contracts with many of the farmers BP took advantage of the regime of terror brought about by the army and paramilitaries, the lack of education of the farmers, the lack of available legal representation in the area - and even took steps to sideline the obtaining of legal advice when it was available."

Within a few months of the completion of the pipeline, the farmers say, the land could no longer support them and the presence of the army made their homes dangerous places to live. Many felt they had no choice but to leave the country for the hope of work in nearby Zaragoza, Segovia and Medellin. But instead, most ended up unemployed and living in the shanty towns, unable to properly support their families.

The farmers say their only hope for compensation is to bring a legal case for negligence against BP in the High Court, because attempts to try to resolve their claims in Colombia have been frustrated and have put them at risk from the paramilitaries.

Mr Day is determined that BP should face up to its responsibilities in a British court. "BP has suggested that our clients should be able to gain access to justice within the Colombian judicial system," he said.

"It is now some 7-8 years since the events occurred which led to these claims. In that time despite trying to do the very thing they have suggested, the Colombian lawyers for our clients have been either killed or forced to flee the country, and their claims have disappeared into the Colombian courts.

"Our clients might be forgiven for coming to a different view to the one they have taken."

But BP says it has acted responsibly. In a statement issued yesterday the company says: "BP believes that the pipeline companies (and the BP companies holding minority interests in the pipelines), have fulfilled their obligations, both from a legal and a Corporate Social Responsibility standpoint. The land-owners neighbouring the Rights of Way of the Ocensa and ODC pipelines were fairly compensated during construction, and the land has been theirs to use ever since.

"Third-party validation, such as the Colombian Ministry of the Environment's report, supports BP's position. BP's lawyers are in correspondence with Leigh Day & Co, and the pipeline companies continue to implement their social investment strategies throughout."