Mr Trimble took ministers by surprise by declaring, within hours of his unexpected victory in the party leadership contest, that the decommissioning of republican weapons would not automatically permit Sinn Fein to join all-party talks on the future of the province.
"Handing in some weapons may not be enough because it may not establish a commitment to exclusively peaceful methods," he told a Belfast news conference. "If you are committed to exclusively peaceful means, that means you don't have private armies, you don't have weapons."
Indicating that disbandment of the IRA and other paramilitary groups would eventually be required, the new Unionist leader insisted: "At some point, the issue of not just the weapons but the existence of private armies has to be dealt with."
Downing Street sources disclosed that senior officials of the Irish and British governments are to meet in London tomorrow with the aim of breaking the logjam that followed the postponement of agreement between them on an international commission to handle the decommissioning of arms.
"They will look at the issues," said a Dublin source. "The election of David Trimble will be the backdrop to that." If Mr Trimble's tough language dismays them, Irish ministers take heart from John Major's sense of urgency in pushing ahead with talks despite the setback of the cancelled summit last week.
Mr Trimble, for his part, said he wanted quickly to meet political leaders throughout Ireland and Britain. He will also meet Bill Clinton when the US President visits Ireland in November. Judging from his comments yesterday, his message to them will be uncompromising. He excoriated Sinn Fein, arguing: "The mere fact that we have had a ceasefire for a year does not show a commitment to exclusvely peaceful methods."
The threat of a resumption of violence from the IRA is widely believed at Westminster to have been the reason for Dublin's unexpected decision to back down from a summit intended to agree the ways and means to decommission terrorist weaponry. The proposed international commission would have reported on arrangements for decommissioning within about two months, and ministers' "exploratory dialogue" with Sinn Fein would have continued in the meantime. Downing Street insists Mr Major is still committed to this "twin-track" approach.
However, the deep suspicions voiced by Mr Trimble make it unlikely that the Unionists will join in this phase of the process. Andrew Hunter, chairman of the Northern Ireland Committee of Tory backbench MPs, said: "At the moment, there appears to be something of an impasse but I don't think we will find the UUP being particularly pro-active in the search for a way round the impasse."
Whereas his predecessor, James Molyneaux, operated mainly behind the scenes, he added: "I think the UUP rank and file want a stronger leader with a physical presence; hence the move to David Trimble."
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