Sinn Féin set out for talks at Leeds Castle in Kent yesterday accusing the British and Irish governments of being ill-prepared and the DUP of refusing to talk directly to republicans.
Mr Mitchel McLaughlin, the Sinn Féin chairman, said the largest unionist party needed "to face up to the challenges if we are to have a successful outcome".
Addressing a press conference at Sinn Féin's Falls Road office, Mr McLaughlin, accompanied by Ms Michelle Gildernew, Ms Caitriona Ruane and Mr Conor Murphy, insisted they were prepared to negotiate a deal with unionists and the two governments.
But he warned: "If Leeds Castle are to have any hope of success closure is needed on many of the key outstanding issues. As we prepare to fly to England, the work that needed to be done has not been done."
He criticised the British government for not initiating a judicial inquiry into collusion and the killing of Mr Pat Finucane, and accused both governments of contemplating concessions to the DUP and that party's anti-agreement stance.
"We are concerned that the governments may be tempted to make significant concessions to the DUP's anti-agreement agenda and, in particular, their attempts to undermine the core principle of power-sharing and the all-Ireland architecture of the agreement. This is unacceptable," he said.
He returned to his recent criticism of "persistent anti-peace process activities on the part of securocrats and the Northern Ireland Office".
He added: "Despite these deep worried, Sinn Féin travels to Leeds Castle to do our best to find agreement. There are enormous gaps that have to be bridged by the two governments and the DUP, but in particular the British government."
The Ulster Unionist leader, Mr David Trimble, said he hoped the talks proved to be the "last lap". Mr Trimble said he was certain it was possible to reach a deal on restoring devolution, but it depended on others living up to their commitments.
He said republicans were "perfectly capable of saying: 'We are going to end all paramilitary activity and ensure that what exists are operating peacefully and democratically'," he said.
"They need to tell people why they have been stringing out the process for the last two years, why they have been frustrating the operation of the political process and we have to ask the government: 'Why have you been allowing them to do this'?"
Other unionists contacted by The Irish Times did not believe the DUP was ready to do a deal with republicans and others, and cited what they say are tensions between strands of opinion within the DUP. One said it was up to the British government to recognise this and to push the largest unionist party in the direction of a settlement.
SDLP Assembly members said they travelled to Leeds Castle more in hope than expectation. One said that republicans needed to deliver a clear end to the IRA's "war".
The discovery of an alleged bugging device at Sinn Féin's Connolly House offices in Belfast is being raised with the President of the European Parliament, Mr Josep Borrell.