The Ulster Unionist Party leader, Mr David Trimble, has vowed he will not give up, despite his party's bruising defeat in the crucial South Antrim by-election.
Mr Trimble conceded the defeat of his party candidate, Mr David Burnside, by the anti-agreement DUP candidate, the Rev William McCrea, was a setback and a disappointment. But he insisted he and his colleagues would continue to work the Belfast Agreement.
"Yes, we've had a setback but we are not quitters. We knew this was not going to be easy. We're deeply disappointed we did not do better but we don't give up."
Mr Trimble spoke to reporters yesterday outside a hotel in Templepatrick, Co Antrim, where his party had gathered to discuss business at the Belfast Assembly and the by-election defeat. He said several factors were behind his party's disappointing performance.
These included poor voter turnout and a protest at the Patten proposals for changes to the RUC.
"We think people should listen to that protest vote, but the people who should listen to it are primarily the (British) government, primarily those nationalists and republicans who have been putting far too much pressure on the Patten issue, not appreciating the extent to which they were distorting the agreement.
"I think there has been a failure to appreciate by some nationalist-republicans the fact that Patten made mistakes by not sticking to the terms of reference set out in the agreement."
Mr Trimble said his party looked forward to making further progress on the issue when the Police Bill goes before the House of Lords next month.
Responding to calls from his party colleague, Mr Jeffrey Donaldson, for the UUP to withdraw from the Executive of the Belfast Assembly, Mr Trimble said the party was quite prepared to listen to, and consider, the views put forward by leading members.
"If there's a coherent alternative which promises better government for the people of Northern Ireland, then of course we will look at it. But at the moment I doubt if that is the case."
He acknowledged difficulties and differences of view within his party. "We're engaged in difficult matters, in difficult policy issues. It would be incredible if everybody was agreed all the time.
"Of course there are differences. But one thing that people should note, and that is the determination of this leadership to deliver, and in terms of what we've done in the agreement and since the agreement."
He compared the party's vote yesterday, at 35 per cent, with its 29 per cent vote at the Belfast Assembly elections in 1998.
In those elections, anti-agreement unionists combined got 15,000 votes to 12,000 for pro-agreement unionists, a majority of 3,000, he said. Yet Mr McCrea's victory over Mr Burnside was only by 822 votes.
"That actually shows that there is still clear support for what we are doing."