Martin McCauley, Niall Connolly and James Monaghan rejected allegations that they belonged to the IRA and called the case against them “fraudulent and misleading”.

The trio had previously refused to appear at the trial, which began a year ago, but they agreed to the judge’s request that they attend the closing stages.

They arrived in handcuffs and were whisked through a back entrance while police drove a windowless blue van to the main entrance to create a distraction.

The men had not been seen in public since they were arrested in August of 2001 on charges that they taught bomb-making techniques to guerrilla fighters from the Revolutionary Armed Forces of Colombia (Farc).

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The three appeared pale but relaxed and conferred occasionally with their lawyers. They took the stand one by one, reading ten-minute statements. Mr Monaghan, grey-haired, bespectacled and wearing a turqouise shirt, said: “I am not a member of the IRA. The charge of training the Farc is a false charge. The training never happened and I and my friends are therefore not guilty. We travelled to Colombia principally to see the peace process but also to enjoy a holiday.”

Mr McCauley played down being charged with weapons possession in Northern Ireland and defended his decision to travel to Colombia on a false passport. He said that it was “nothing more than a desire to travel unhindered,” given threats and violence against former “political prisoners”.

Mr Connolly, who served as a Sinn Fein representative in Cuba, read his statement in English and Spanish. He also denied belonging to the IRA and said that the men had wanted to study the peace process. It disintegrated in February, 2002. “This case should never have been brought to this court,” he said.

The case has provoked indignation among many Colombians, who accuse the men of bringing IRA know-how to Colombia’s violent, 38-year civil conflict.

Officials arrested the defendants, all of whom carried false documentation, at Bogotá’s airport as they prepared to board international flights. The three had arrived from San Vicente, a run-down cattle town in rebel territory.

American-assisted forensic tests showed that they had explosive residue and drug particles on their clothes, although a less sophisticated test by Colombian police contradicted those findings.

The men’s lawyers are expected to give closing arguments today.

Once the hearings end, the judge has 15 days to return a verdict.

Prosecutors have urged the judge to return guilty verdicts and to give an “exemplary” sentence of 20 years for each defendant.

Financed through drug profits, Farc has used increasingly brutal tactics over recent years. Recently, the rebel army bombed a social club in Bogotá and paid an unsuspecting ten-year-old boy 30 cents to ride a “bicycle bomb” past a police checkpoint. The boy died instantly when rebels detonated the bomb by remote control.

General Jorge Enrique Mora, head of the Colombian Armed Forces, referred to the three Irishmen as “bandits”, evoking a label that he often applies to his country's Marxist rebel factions. He said: “Now (the men) are coming out with the story that they were teaching English to the Farc? As if we Colombians would buy that story.”

Defence lawyers said that such comments made it impossible for their clients to receive a fair trial.

As proceedings opened, the defendants refused to leave their cell, resulting in a scuffle with guards. Later, prosecutors asked for a postponement while they tried to track down a missing key witness. Another witness, a Farc deserter, appeared in court wearing a bulletproof vest.