The Government was holding on to the hope that the Unionists would wish to avoid precipitating a crisis. Mo Mowlam, the Northern Ireland Secretary, declared that the Unionists were "still talking - they are not walking" after a 75-minute meeting in Downing Street. Mr Trimble said: "We will not shirk our responsibilities. We are not in the mode of walking out."
In spite of the IRA ceasefire, the Unionists are holding out for written guarantees that decommissioning of terrorist weapons will take place during the cross- party talks, before they sit down with Sinn Fein.
Mr Trimble added that he would be consulting the community in Ulster. That was seen in Dublin as an ominous sign that the Unionist leaders are preparing to hold out, and seek the backing of the Unionist community in Ulster to avoid being blamed for the deadlock.
The crunch may be avoided tomorrow by putting off a vote in Belfast on the joint Anglo-Irish plans for decommissioning. But the two governments have a fall-back plan, to carry on with proximity talks, in which the parties would not be sitting at the same negotiating table. The results would be put to referendums next May in Ireland, North and South.
Mr Blair is today expected to make a renewed appeal by telephone to the Ulster Unionist leader in Belfast. However, Mr Trimble said yesterday that verbal assurances from Mr Blair were not enough.
The former Canadian general John de Chastelain, who will be appointed chairman of the decommissioning body, last night confirmed it could be up and running before the substantive talks begin in September.
Meanwhile, the political fall-out from the IRA ceasefire continued in Belfast, when one of the small unionist parties walked out of the peace talks in protest at the presence of a Sinn Fein delegation.
The Sinn Fein team, led by the party chairman, Mitchell McLaughlin, arrived at the castle buildings in Stormont to set up offices for their likely entry into the talks on 15 September.
The UK Unionist party, led by MP Robert McCartney left the building within minutes, claiming it had always promised that it would not take part in negotiations with any party which supported violence or associated with any group which still held the means for violence - a clear reference to the controversial issue of decommissioning weapons.
The Democratic Unionist Party, led by Dr Ian Paisley, stayed away from Stormont yesterday and is likely to make a decision on its stance after talks with Tony Blair today.
Mr McLaughlin, who was accompanied by the leading Sinn Fein figure Gerry Kelly, a convicted IRA terrorist, said the door should be kept open for Unionists to re-enter the process.
He said: "In the past, Unionists have walked out only to return at a later date."
He emphatically denied Unionist claims there had been a secret deal between themselves and the British government to facilitate the ceasefire and let them into the talks.
"We're not interested in secret deals," he said.
The security presence throughout Northern Ireland remained tight yesterday after warnings from two Republican splinter groups, including the Irish National Liberation Army, that they were unhappy with the ceasefire to which they were not party.
The Government may try to reassure the Unionists with a letter of clarification today, similar to that sent to Sinn Fein, which helped to pave the way for the ceasefire. But Mr Trimble said if there was no "significant change", his party would vote down the decommissioning proposals at the meeting in Stormont tomorrow.
Downing Street said that the two deadlines, for the start of talks on 15 September, and the end of talks in May, 1998, were not negotiable.
Holding out hope that the crisis could be averted, Ms Mowlam said: "They are not walking, we are still trying, so the talks process is still going."
The Prime Minister's office said: "The important point from our point of view is that there was a clear decision on their part not to walk out of the talks."
The Ulster Unionists object to the wording of the joint government proposals to bring about "due progress" on decommissioning alongside progress on the talks.
Downing Street said it would be "very difficult" to meet the Unionists' demands to amend the joint document, agreed by the Irish and British Governments.
History at Stormont, page 8
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