"It will be a big culture shock for our people to sit around the negotiating table with Sinn Fein. They don't know what to expect," confesses one Ulster Unionist politician. At 2 p.m. at Stormont today will come the moment many unionists have been dreading for years.
David Trimble is expected to lead his troops into a face-to-face meeting with a party they have long regarded as the political wing of the IRA. "It will be a sombre occasion," says the source. "Nobody is looking forward to it. Nobody will relish it but it is something which just has to be done." The UUP insists it is entering talks primarily to call for Sinn Fein's expulsion on the grounds of the IRA's admission that it has "problems" with the Mitchell Principles and last week's bomb by the Continuity IRA which, Mr Trimble says, could not have been carried out without the approval of the Provisionals.
The first item on the talks agenda is the UUP's indictment of Sinn Fein. But Mr Trimble is no fool. He knows that after "careful deliberation", his motion will fail. There is no way that the two governments will eject republicans from the process. Sinn Fein is there to stay.
The UUP leader is using the indictment as a means of entering the talks without leaving himself open to the charge of capitulation. By joining the process without prior IRA decommissioning, he has moderated his stance considerably and is vulnerable to shouts of "sell-out" by the DUP and Mr Bob McCartney's UK Unionist Party which have both withdrawn from talks.
While the two governments and the other parties will undoubtedly welcome Mr Trimble's decision, there must be caution about what is attainable. It is much too early to view him as a unionist de Klerk. The UUP leader still conveys the impression that the party is entering the talks to score points against republicans, not to reach an historic settlement with nationalism.
"We are not offering our community leadership," complains a liberal unionist councillor. "I feel that we are going to talks very reluctantly and not because we want to but because everyone we spoke to during our consultation process told us to go and the public clearly wants us to be there.
"The public is leading us and it should be the other way round. I can only hope that once we are there, our fears and suspicions will be overcome and we will get involved, honestly and sincerely, in trying to reach a settlement that everyone can live with."
But although opinion polls show that the unionist community wants its leaders at talks, making the compromises that nationalists will demand over the coming eight months is another matter. Sinn Fein has insinuated that a settlement based on the Framework Document is its bottom line. The UUP has already rejected the document.
Even if the UUP signs up to a deal which includes some role for Dublin and a range of cross-Border bodies, will republicans ultimately accept that Northern Ireland will remain within the UK so long as a majority of its citizens wish? And if Mr Gerry Adams and the Sinn Fein leadership are prepared to agree to what would in effect be a partitionist settlement, will they be able to convince their supporters to follow suit?
Unionist and loyalist politicians might be prepared to countenance certain reforms regarding policing, a bill of rights, and the prisoners issue but they are still unwilling to agree to anything which they believe would weaken the Union.
Weakening the Union is Sinn Fein's raison-d'etre for entering talks. The loyalist paramilitaries say the Union is safe. The IRA insists everything is up for grabs.
Nobody obtains everything they want from negotiations, but on the constitutional issue one side will inevitably be more disappointed than the other when talks conclude. The question is whether they can live with their disappointment without returning to violence. Only time will tell.