As three men go before a Colombian judge today, will their fate seal the course of peace in Ireland?

Three Irishmen face hearings today on their alleged involvement with Colombian narco-terrorists, in an episode which has continued to inflict major damage on the Irish republican movement.

They will appear before a Colombian judge, accused of instructing drug-funded rebels in terrorist tactics and explosives in the country's southern jungles. If convicted, they face 15 or more years in jail, while back in Ireland, Sinn Fein and the IRA will be confronted by a new surge of pressure to explain just what republicans were doing in the company of the Revolutionary Armed Forces of Colombia (Farc).

Niall Connolly, James Monaghan and Martin McCauley were travelling under false passports when they were arrested in Colombia in August last year. Mr Monaghan, a senior republican figure jailed 30 years ago on explosives offences, is a former member of Sinn Fein's national executive.

Their impending trial comes during a particularly sensitive part of the Irish peace process. The Ulster Unionist Party is threatening to pull out of government with Sinn Fein because of what it describes as "the failure of Sinn Fein-IRA to honour their commitment to exclusively peaceful and democratic means". The Colombian episode is one of the factors regularly cited by Unionists as evidence that the IRA has not abandoned terrorism. Convictions in Colombia will be used by hardline Unionists to step up their demands to pull out of a government which includes Sinn Fein.

The most serious allegation is that while Sinn Fein talked peace in Belfast the IRA was hard at work an ocean away, using a remote jungle to test and develop fearsome new weapons to be ready for a future resumption of violence.

The alternative and more benign explanation is that IRA leaders have been committed to peace all along, and were allowing more militant elements in the ranks to work on projects which were never intended for practical use in the UK.

John Reid, the Secretary of State for Northern Ireland, who has described the problems facing the peace process as grave, yesterday emphasised the credibility gap between republicans and Unionists in his speech to the Labour Party conference.

Addressing himself to republicans, Mr Reid declared: "We recognise and welcome the steps you have taken and we know how difficult it was for you. But if you want partnership with Unionists to be sustained, then you need to convince them, to reassure them. You cannot continue to ride two horses at once, especially if the two horses are as far apart as violence and democracy. The people of Northern Ireland are asking you now to have the courage of your democratic convictions. Complete your journey to democracy."

London, Dublin and Washington all operate on the theory that the leadership of Sinn Fein is genuinely pursuing peace. Indeed, Mr Reid told republicans yesterday: "We believe that your leadership is committed to pursuing its aims for a united Ireland through democratic means."

But the Colombian adventure remains unexplained. Although one of the three, Mr Connolly, represented Sinn Fein in Cuba for some years, the party's stance is that it has "no case to answer" in relation to Colombia. The IRA, after a period of silence, said there had been "a lot of ill-founded and mischievous speculation" about the arrests. It added: "We wish to make it clear that the Army Council sent no one to Colombia to train or to engage in any military co-operation with any group. The IRA has not interfered in the internal affairs of Colombia and will not do so. The IRA is not a threat to the peace process in Ireland or in Colombia."

But these assertions did not ease any of the pressure on republicans, since few could think of an innocent explanation for the venture. Among the doubters has been Richard Haass, who directs US policy on Northern Ireland. He said flatly: "Speaking personally, I am quite sceptical of that denial." The Bush administration was particularly angry when the Farc connection came to light. The US regards Farc as narco-terrorists who export huge amounts of drugs to America.

The embarrassment of Irish republicans grew after the 11 September attacks in the US, which came within weeks of the Colombian disclosures. There was relief when Washington decided not to class the IRA as an anti-US terror group.

A fresh wave of opprobrium swept over republicans during the summer when a Farc bombing and mortar campaign claimed scores of civilian lives in Colombia. The Colombian authorities said the bombers had used new techniques which it alleged had been passed on by IRA personnel.

Mr Haass subsequently said he believed the IRA had taught new techniques to Farc, some of whose operations now had the hallmarks of IRA operations. But this did not alter the American line – which is close to that adopted by London and Dublin – that no severe penalty should be exacted on republicans. But the absolute proviso attached to this is that the Colombian connection must be completely severed.

The episode also damaged republicans in Irish America, particularly among the powerful business figures who have contributed so much to Sinn Fein in terms of both money and support. A number have publicly and heavily criticised the involvement in Colombia.

Republicans have always steered clear of the drugs trade. While government agencies do not believe the Colombian episode had anything to do with procuring drugs, the fact of consorting with what are regarded as narco-terrorists has tainted the reputation of the republican movement.

Campaigners for the three men say they cannot expect to receive a fair trial under a regime whose political and military leaders have already publicly asserted their guilt. The trial will be closely watched for the emergence of reliable information on what exactly was going on during this mysterious period.

IRA CONNECTIONS AROUND THE WORLD

The Irish republican movement has had connections of various types with parties, groupings and, in some cases, governments in many parts of the world.

Diverse purposes were served by this approach. It helped keep up local morale, produced a sense of international solidarity and on some occasions provided weapons for the IRA. Probably the warmest relationship exists between Sinn Fein and the Basque separatists, the two groupings having a distinct sense of comradeship.

In recent years Sinn Fein has put a great deal of effort into developing its relations with the US, courting Bill Clinton and keeping in close touch with the Bush administration.

This relationship often sits uneasily with the previous approach of republicans who, prior to the peace process, regarded themselves as part of an international revolutionary fraternity.

But other links were based on a paramilitary basis. Neither Sinn Fein nor the IRA has any great fellow feeling for Farc, which leads observers to assume the relationship with rebels is concerned purely with weapons.

A similar pattern was seen in the 1970s and 1980s, when republicans courted Colonel Gaddafi's Libyan regime. Although there were unconvincing attempts to claim policy similarities, the primary purpose was to get guns. This led to major shipments reaching Ireland from Libya in the 1980s.

Republican sympathy with the Palestinian cause is demonstrated by the many murals in Belfast proclaiming support for the PLO, although that organisation denies any military involvement with the IRA.