Orlando Ordoñez no longer looks like a guerrillero. He is clean-shaven, with suit, shiny boots and long hair slicked into a neat ponytail. Calloused hands and a worn expression on his broad face are the only clues to his past: Ordoñez spent ten years rising through the ranks of the Revolutionary Armed Forces of Colombia (Farc), Latin America's oldest and most powerful guerrilla army. By the time he left in 2005, he was, as describes himself, a high-ranking comandante, managing millions of dollars of the group's profits from extortion and drug trafficking.

Ordoñez experienced the moral decline of the Farc from the inside. He joined as an idealistic 28-year-old, attracted by the organisation's revolutionary agenda. "When I joined, being a guerrillero was a source of pride," he says. "We had the respect of the Colombian people." Initially, he looked after a small territory where peasants grew crops including coca, and the Farc charged the drug traffickers a tax for the service. It was only in the late 1990s that he realised the organisation was increasingly producing and trafficking drugs itself. "The ideology was changing."

His disillusionment grew over time. He discovered that other comandantes had been abusing, threatening and displacing peasants in the areas they controlled. "Our reputation in those communities suffered very badly." Then he was given a promotion, and moved into a position where he was expected to buy influence with politicians, businessmen and police. "I was unhappy with my life, and with the Farc," he says. He took the potentially life-threatening decision to desert and handed himself in to the army.

Ordoñez is now training at a community television station, and hopes to persuade others to demobilise. "I want all the guerrilleros to know that if they want to really make a difference, they should rejoin Colombian society. If they want to work for the left-wing cause, this is a democracy and they are free to do that."

At present, the Colombian left is in a sorry state. Unlike much of the rest of Latin America, where centre-left and left-wing administrations have become increasingly common, Colombia is governed by a right-wing, militaristic, pro-business president, Álvaro Uribe. After winning two elections by large majorities on the promise that he would smash the guerrillas with a "strong hand", he saw his popularity recently hit 84 per cent. The opposition is floundering. This is even though the country has one of the most unequal societies in the world: its cities are filled with shiny 4x4s, designer beauty queens and chichi shopping malls, but in its slums and rural areas 50 per cent of the population lives in poverty.

No support

Those on the left in Colombia have one expla nation for their lack of popularity: the Farc effect. "It is our greatest problem," says José Sanín Vásquez, director of the trade union research institute Escuela Nacional Sindical. "If being on the left means wanting change, then the Farc has become ultra-right-wing. It is a great obstacle to change in this country." It is a mark of how far the Farc has fallen that, despite great injustices in Colombia, it commands almost no support from any section of society. In a recent Gallup poll, all but 3 per cent of Colombians said they had an unfavourable opinion of the Farc.

Trade unionists, human rights campaigners, community leaders and left-wing politicians all have the same complaint: their credibility is continually damaged by insinuations in politics and the media that they are "guerrilla sympathisers" (Uribe has made a habit of smearing his critics, including Amnesty International and other NGOs, in this way). "It suits the government to describe the Farc as left-wing, as that way it stigmatises the opposition," says Sanín. "It suits the Farc because it gives it a certain legitimacy. Meanwhile, the real left in Colombia is completely squashed between the two."

The Farc was founded in 1964, and headed by a peasant leader and member of the Communist Party known as Manuel Marulanda, or "Tirofijo". Its members came from existing peasant militias, but during the 1960s and 1970s it adopted a Marxist ideology. As other guerrilla groups in Colombia and across Latin America have been defeated or drawn into mainstream politics, the Farc has continued to wage an implacable war against the Colombian state, fuelled increasingly by profits from the drugs trade. It also specialises in kidnapping and extortion, with some of its hostages - most notoriously the former presidential candidate Ingrid Betancourt - kept in jungle hideouts for years.

The impact of the guerrilla movement in Colombia has been particularly devastating because it has given rise to an array of right-wing paramilitary groups, which sprang up around the country during the 1990s. Their aim was to protect the interests of large landowners and they were brutally dismissive of the rights of the civilian population, taking revenge on anyone they considered to be a guerrilla supporter. The armed groups from left and right have contributed to a bloody and seemingly intractable civil war, in which the value of human life has been disregarded by both sides. Tens of thousands of Colombians - usually from the poorest communities - have been killed, and three million more displaced; the country has the world's second-largest internally displaced population, outstripped only by Sudan's.

Harsh discipline

The highest estimated figure for Farc membership stands at 30,000, though the Colombian government claims that numbers have fallen to around 8,000. Its soldiers are drawn largely from the most deprived social groups, attracted by the offer of a basic wage. "I always liked guns, and what's more I come from a very poor family. The Farc told me they would help me if I joined," says Francisco, a softly spoken 22-year-old from a peasant family in the Antioquian region, who joined the group when he was 17. Like many Farc foot soldiers, he is illiterate. "They taught me all about the ideology and to sing the revolutionary anthems. They taught us that the Farc would bring the Cuban Revolution to Colombia. Once I was trained, they gave me a gun and set me missions, like collecting a certain amount of base [coca paste] from a particular area, and bringing it back to the camp."

The conditions for recruits are harsh: the group operates from bases deep inside Colombia's vast, dense jungles, where disease is rife and resources are scarce. Discipline is brutal; those who break the rules are subjected to trials, or "war councils". "When somebody broke the rules, they would tie them up and present them in front of the group to decide their punishment," says Francisco. "If they had a good record, they might be given a chance. If they had stolen food from the store tent or something, and had done it a number of times, they would be given the maximum penalty. Often they would just tie people up and punish them for nothing."

In Colombia, it has long been widely accepted across the political spectrum that although the Farc continues to use Marxist rhetoric, it has abandoned any claim to political legitimacy. "The foot soldiers are still taught the ideology, and believe it," says Jaime Echevarría, another former member who did not want his real name published. Jaime has a university education, but had lost his job and was destitute when he was recruited to the Farc's urban division. "But to judge by my contact with the higher ranks and the secretariat [the Farc's seven-man governing body], I would say they have left that behind. They are businessmen."

The increasingly public alliance between the Farc and the Venezuelan president, Hugo Chávez, which reared its head last month, has served to bolster Uribe's position and further demoralise the Colombian left. The extent of the collaboration between the two is a matter of debate - the Colombian government claims to have evidence that Chávez has provided the Farc with funds, although he denies this. He has, however, made no secret of his political support (as reported in the NS of 11 February). The two countries were brought to the brink of war in March following an illegal raid by Colombian troops into Ecuadorian territory, during which one of the Farc secretariat, Raú Reyes, was killed. Ecuador was understandably furious, but Chávez went further, ordering troops to the border and announcing a minute's silence in Reyes's honour.

"Venezuela does not support the Farc, but Chávez has made a strategic alliance with them," says Fernando Gerbasi, formerly Venezuela's ambassador in Colombia and now a professor of international relations at the Universidad Metropolitana in Caracas.

Having turned its back on the political arena at home, the Farc has focused on building up international support, effectively playing on tensions between right-wing Colombia and its "21st-century socialist" neighbour. With a huge amount of military aid pouring into Colombia from the United States - around $5bn since 2000 - its neighbours, with comparatively scant military resources, understandably fear that the country has become a foothold from which the US can extend its influence in the region.

"The danger is that the US would like Colombia to be its proxy for an anti-Chávez campaign," says Rodrigo Pardo, editor of the Colombian political magazine Cambio. "That would be disastrous for regional relations."

Strengthening Uribe

Gustavo Petro, a senator for Colombia's left-wing opposition Polo Democrático Alternativo party, describes himself as a personal friend of Chávez. He believes that the Venezuelan president allowed himself to be persuaded that the Farc offered the only way of challenging the Uribe administration, and protecting himself against American aggression.

"This was a grave error, and if he had consulted us it never would have happened," Petro says. "The relationship between the Farc and the Latin American left represents a mortal danger for the left." He despairs that the crisis has once again boosted the popularity of the already unchallengeable Uribe. "It has affected the left in Colombia profoundly. We have been damaged - thankfully, we were spared annihilation because we did not ally ourselves closely with Chávez."

Meanwhile, the Uribe administration continues to implement controversial policies, virtually unchecked by a serious opposition. Colombia is opened up to business while trade unionists fear for their lives; millions of dollars are poured into the military while the displaced population is abandoned to live in squalid poverty. The government offers cash incentives for the murder of suspected guerrilleros - last month, it gave a $2.6m reward to a Farc soldier who killed another member of the secretariat and delivered his hand to the authorities in a plastic bag.

"There is a lot of work for the left to do in this country," says Petro with a weary smile."