THE Prime Minister will today urge Ulster Unionist leaders to seize the opportunity presented by the IRA ceasefire to talk peace with Sinn Fein despite their fears over decommissioning.

Unionist anxieties about the nationalists' goodwill were reinforced by comments from Sinn Fein's chief negotiator, Mr Martin McGuinness, who said he did not believe the IRA intended to hand over a single bullet.

Mr McGuinness said: ''The IRA has said that it will not decommission a single bullet and I have not heard any statement from it saying it has changed its position on that.''

As Mr Blair prepared for the crunch talks at Downing Street, it emerged that former Taoiseach Albert Reynolds was involved in discreet diplomatic moves which brought about the second IRA ceasefire that began at noon yesterday.

Informed sources in Dublin confirmed that Mr Reynolds, the co-architect with Mr John Major of the 1994 ceasefire, had met key republican figures ahead of the IRA's decision.

However, even before the appointed hour of Mr Blair's meeting with Ulster Unionist leader David Trimble, important sections of the Unionist community were voicing grave suspicions about the IRA and Sinn Fein's commitment to peace.

They were also anxious over whether the Government had conceded too much on arms to encourage the ceasefire and so clear Sinn Fein's path to the Stormont talks.

Ulster Unionist deputy leader John Taylor said he could not take part in talks with Sinn Fein under the ill-concealed threat of a resumption of violence if nationalists were unhappy with the direction the talks were taking.

In a clear indication that the UUP may refuse to take part in talks unless they are accompanied by decommissioning, Mr Taylor insisted his party would not talk to any party which brought a gun to the negotiating table.

It was up to the party to decide what approach to take to the talks, he said.

However, he added: ''I personally could not take part in talks with Sinn Fein with a gun to my head.

''We will not talk to a party which is not totally committed and exclusively committed to peaceful means - and demands the right to keep a gun at the table so we agree with what they are saying.''

Mr Taylor said the present ceasefire was just a restoration of the last one which had been a ''fraud''. He suspected that the Government had succumbed to an IRA demand that multi-party talks should proceed without decommissioning.

He said: ''What we are asking is for the Government to stand firm over its previously stated position, that, in accordance with the Mitchell report and principles, decommissioning shall take place in parallel with the talks.''

It appears that Mr Blair will attempt to reassure Unionists by promising early confirmation of the full membership of the body which will handle decommissioning during the talks, and by telling them that it will be up and running before the talks begin.

It is understood that it will be chaired by Mr John De Chastelain, former chief of the Canadian defence forces.

If Mr Trimble is unimpressed by Mr Blair's assurances, his party could vote on Wednesday against the latest UK-Irish decommissioning proposals which, they have said, are insufficiently specific about the pace at which decommissioning should proceed.

Democratic Unionist Party deputy leader, Mr Peter Robinson, made it clear that decommissioning was also the most urgent issue for his party.

Mr Robinson said: ''The basis for Sinn Fein entry to a talks process should be that it has undertaken a permanent and complete cessation of its