Spain and Portugal being the principal ports of entry. The drug's value on European streets is some £7.5bn a year.

Thirty per cent of the 600 tons of cocaine smuggled from Colombia each year goes through Venezuela. Most of that 30 per cent ends up in Europe, with Spain and Portugal being the principal ports of entry. The drug's value on European streets is some £7.5bn a year.

The infrastructure that Venezuela provides for the cocaine business has expanded dramatically over the past five years of Chávez's presidency, according to intelligence sources. Chávez's decision to expel the US Drug Enforcement Administration from his country in 2005 was celebrated both by Farc and drug lords in the conventional cartels with whom they sometimes work. According to Luis Hernando Gómez Bustamante, a Colombian kingpin caught by the police last February, 'Venezuela is the temple of drug trafficking.'

A European diplomat with many years of experience in Latin America echoed this view. 'The so-called anti-imperialist, socialist and Bolivarian nation that Chávez says he wants to create is en route to becoming a narco-state in the same way that Farc members have turned themselves into narco-guerrillas. Perhaps Chávez does not realise it but, unchecked, this phenomenon will corrode Venezuela like a cancer.'

The deserters I interviewed said that not only did the Venezuelan authorities provide armed protection to at least four permanent guerrilla camps inside their country, they turned a blind eye to bomb-making factories and bomber training programmes going on inside Farc camps. Rafael - tall and lithe, with the sculptured facial features of the classic Latin American 'guerrillero' - said he was trained in Venezuela to participate in a series of bomb attacks in Bogotá, Colombia's capital.

Co-operation between the Colombian guerrillas and the Venezuelan government extended, Rafael said, to the sale of arms by Chávez's military to Farc; to the supply of Venezuelan ID cards to regular guerrilla fighters and of Venezuelan passports to the guerrilla leaders so they were able to travel to Cuba and Europe; and also to a reciprocal understanding whereby Farc gave military training to the Bolivarian Forces of Liberation, a peculiar paramilitary group created by the Chávez government purportedly for the purpose of defending the motherland in case of American invasion.

Chávez's contacts with Farc are conducted via one of the members of the organisation's leadership, Iván Márquez, who also has a farm in Venezuela and who communicates with the President via senior officials of the Venezuelan intelligence service. As a Farc deserter who had filled a senior position in the propaganda department said: 'Farc shares three basic Bolivarian principles with Chávez: Latin American unity; the anti-imperialist struggle; and national sovereignty. These ideological positions lead them to converge on the tactical terrain.'

The tactical benefits of this Bolivarian (after the 19th-century Latin American liberator, Simón Bolívar) solidarity reach their maximum expression in the multinational cocaine industry. Different methods exist to transport the drug from Colombia to Europe, but what they all have in common is the participation, by omission or commission, of the Venezuelan authorities.

The most direct route is the aerial one. Small planes take off from remote jungle strips in Colombia and land in Venezuelan airfields. Then there are two options, according to intelligence sources. Either the same light planes continue on to Haiti or the Dominican Republic (the US government says that since 2006 its radar network has detected an increase from three to 15 in the number of 'suspicious flights' a week out of Venezuela); or the cocaine is loaded on to large planes that fly directly to countries in West Africa such as Guinea-Bissau or Ghana, from where it continues by sea to Portugal or the north-western Spanish province of Galicia, the entry points to the EU Schengen zone.

A less cumbersome traditional method for getting the drugs to Europe in small quantities is via passengers on international commercial flights - 'mules', as they call them in Colombia. One of the guerrilla deserters I spoke to, Marcelo, said he had taken part in 'eight or nine' missions of this type over 12 months. 'Operating inside Venezuela is the easiest thing in the world,' he said. 'Farc guerrillas are in there completely and the National Guard, the army and other Venezuelans in official positions offer them their services, in exchange for money. There are never shoot-outs between Farc and the guardia or army.'

Rafael said he took part in operations on a bigger scale, their final objective being to transport the cocaine by sea from Venezuelan ports on the Caribbean Sea. His rank in Farc was higher than Marcelo's and he had access to more confidential information. 'You receive the merchandise on the border, brought in by lorry,' he said. 'When the vehicle arrives the National Guard is waiting, already alerted to the fact that it was on its way. They have already been paid a bribe up front, so that the lorry can cross into Venezuela without problems.

'Sometimes they provide us with an escort for the next phase, which involves me and other comrades getting on to the lorry, or into a car that will drive along with it. We then make the 16-hour trip to Puerto Cabello, which is on the coast, west of Caracas. There the lorry is driven into a big warehouse controlled jointly by Venezuelan locals and by Farc, which is in charge of security. Members of the Venezuelan navy take care of customs matters and the safe departure of the vessels. They are alive to all that is going on and they facilitate everything Farc does.'

Rafael described a similar routine with drug operations involving the port of Maracaibo which, according to police sources, is 'a kind of paradise' for drug traffickers. Among whom - until last week when he was gunned down by a rival cartel in a Venezuelan town near the Colombian border - was one of the 'capos' most wanted internationally, a Colombian called Wilber Varela, but better known as 'Jabón', which means 'soap'. 'Varela and others like him set themselves up in stunning homes and buy bankrupt businesses and large tracts of land, converting themselves almost overnight into personages of great value to the local economy,' a police source said. 'Venezuela offers a perfect life insurance scheme for these criminals.'

This 'tactical' convergence between the Venezuelan armed forces and Farc extends to the military terrain. To the point that, according to one especially high-placed intelligence source I spoke to, the National Guard has control posts placed around the guerrilla camps. What for? 'To give them protection, which tells us that knowledge of the tight links between the soldiers on the ground and Farc reaches up to the highest decision-making levels of the Venezuelan military.'

Rafael told how he had travelled once by car with Captain Pedro Mendoza of the National Guard to a military base outside Caracas called Fuerte Tiuna. He entered with the captain, who handed him eight rifles. They then returned to the border with the rifles in the boot of the car.

Rafael said that members of the National Guard also supplied Farc with hand grenades, grenade-launchers and explosive material for bombs made out of a petrol-based substance called C-4.

An intelligence source confirmed that these small movements of arms occurred on a large scale. 'What we see is the drugs going from Colombia to Venezuela and the arms from Venezuela to Colombia. The arms move in a small but constant flow: 5,000 bullets, six rifles. It's very hard to detect because there are lots of small networks, very well co-ordinated, all of them by specialists in Farc.'

Rafael worked directly with these specialists, both in the arms and the drugs business, until he decided the time had come to change his life. 'In June and July I had received courses in making bombs alongside elements of Chávez's militias, the FBL. We learnt, there in a camp in Venezuela, how to put together different types of landmines and how to make bombs. They also taught us how to detonate bombs in a controlled fashion using mobile phones.'

They were training him, he said, for a mission in Bogotá. 'They gave us photos of our targets. We were going to work alongside two Farc groups based in the capital. The plan was to set off bombs, but as the date dawned I began to reflect that I could not continue this way. First, because of the danger from the military engagements we had with the ELN [another formerly left-wing guerrilla group] on the border over control of the drug routes and, second, because it now seemed to me there was a very real risk of getting caught and I believed I had already spent enough years in jail for the Farc cause. It was also highly possible that the security forces in Bogotá would kill me. That was why at the end of August I ran away and in September I handed myself in.'

A European diplomat who is well informed on the drug-trafficking business generally, and who is familiar with Rafael's allegations, made a comparison between the activities of Farc in Venezuela and hypothetically similar activities involving Eta in Spain.

'Imagine if Eta had a bomb-making school in Portugal inside camps protected by the Portuguese police, and that they planned to set off these bombs in Madrid; imagine that the Portuguese authorities furnished Eta with weapons in exchange for money obtained from the sales of drugs, in which the Portuguese authorities were also involved up to their necks: it would be a scandal of enormous proportions. Well, that, on a very big scale, is what the Venezuelan government is allowing to happen right now.'

'The truth,' one senior police source said, 'is that if Venezuela were to make a minimal effort to collaborate with the international community the difference it would make would be huge. We could easily capture two tons of cocaine a month more if they were just to turn up their police work one notch. They don't do it because the place is so corrupt but also, and this is the core reason, because of this "anti-imperialist" stand they take. "If this screws the imperialists," they think, "then how can we possibly help them?" The key to it all is a question of political will. And they don't have any.'

A similar logic applies, according to the highest-placed intelligence source I interviewed, regarding Farc's other speciality, kidnappings. 'If Hugo Chávez wanted it, he could force Farc to free Ingrid Betancourt tomorrow morning. He tells Farc: "You hand her over or it's game over in Venezuela for you." The dependence of Farc on the Venezuelans is so enormous that they could not afford to say no.'