Mr David Trimble has insisted that unless Sinn Féin "completely and finally" resolves its relationship with terrorism a Border poll is the only way of giving unionists confidence to continue in government with them.
And he declared that a Border poll would reassure unionists that the Belfast Agreement was not "programmed towards Irish unification".
Delivering the annual lecture to the Institute of Directors in London last night, the Ulster Unionist leader and Northern Ireland First Minister said two problems persisted within the political process.
The first was the failure of loyalist paramilitaries to respond "in deed" to IRA decommissioning. The second was that, while mainstream unionists and nationalists wanted to believe the IRA had made a decisive breach with the past, they were continually presented with "contra-indications." Mr Trimble said the IRA continued to engage in beatings and murders.
Moreover, Sinn Féin's "qualified enthusiasm for democracy" was exemplified by its lack of enthusiasm for parliamentary investigations both in the Republic and in the US, where the Sinn Féin president, Mr Gerry Adams, was reluctant to attend hearings into allegations of IRA links to the FARC narco-terrorists in Colombia. The FARC group, Mr Trimble said, had engaged in two major bombings within the last 10 days, "both of which bear uncanny resemblance to IRA actions of the past."
Mr Adams's contempt for the US Congress investigation and parliament, which had given unstinting support for the peace process, was palpable.
The current situation presented the British and Irish governments with a considerable problem, he said, but few people believed casting the Belfast Agreement aside would encourage progress.
However, many unionists had deep reservations about the implementation of the agreement and Sinn Féin's democratic bona fides, and it was in that context that Mr Trimble said he had raised the idea of a Border poll.
Such a poll would give unionists the confidence that their political position within the UK was secure and would also remove the Border question from political debate for the foreseeable future.
He asserted that unless and until Sinn Féin resolved completely and finally its relationship with terrorism at home and abroad, he could see no other way of giving unionists the confidence they needed to continue operating in government with such a party and reassuring them that, whatever else, the Belfast Agreement was not programmed towards Irish unification.
Reflecting on the broader political process since the signing of the Belfast Agreement, the Ulster Unionist leader said paramilitarism no longer thrived, but it had proved stubborn nonetheless, and the transformation of paramilitaries had been partial.
And he suggested that the timing of the IRA's second act of decommissioning had been strongly influenced by the forthcoming Irish election.
On Northern Ireland's economic prospects, Mr Trimble highlighted the fact that unemployment had fallen to 6.3 per cent, well below the EU average, with the number of jobs growing by 10.2 per cent since December 1996.
Although the figures for employment, manufacturing output and manufacturing sales were encouraging, Mr Trimble said much more needed to be done to attract further foreign investment.
He added: "Just as a vibrant economy can assist our moves towards political stability, so, too, can that stability be a major factor in attracting continued investment and progress on an economic front."
Mr Trimble also said that the British government had made a major mistake by failing to link the early release of paramilitary prisoners with paramilitary decommissioning.
It had also allowed itself to be bullied by republicans into an uncritical acceptance of every "jot and tittle" of the Patten report on policing in Northern Ireland, he said.