Democratic Unionist Party leader the Rev Ian Paisley has said that general election results in Northern Ireland represented the "burial" of the Belfast Agreement.
Dr Paisley also warned the incoming Northern Secretary against confronting the unionist electorate.
Speaking at Westminster, where he and his party's eight other MPs are due to be officially sworn in later this week, Dr Paisley cautioned Peter Hain: "Heed the ballot box. Listen to what the people of Ulster are saying. If you're going to come over here to confront the Ulster unionist people, then you're going to fail."
Now leading the fourth largest party in the House of Commons, Dr Paisley's party further bolstered its position as the leading unionist party when it won a record 182 seats in the local government elections compared to 115 for the Ulster Unionists.
The returned Sinn Féin MP for West Tyrone, Pat Doherty, also at Westminster with newly-elected Newry and Armagh MP Conor Murphy to reclaim the party's office facilities, accused Dr Paisley of "his usual bluster".
"Mr Paisley should remember he talks for the DUP, not anyone else," said Mr Doherty.
He said the DUP leader "cannot claim the mantle" of talking for the entire electorate and was not in a position to lecture the incoming Northern Secretary.
"He only speaks for the DUP," said Mr Doherty. "His party got 34 per cent of the people's vote. We got 25 per cent. The SDLP and Ulster Unionists got about 17. If he wants the Assembly back then he is going to have to work with all the parties."
Asked when he anticipated a response from the IRA to the appeal by party president Gerry Adams for it to turn exclusively to constitutional means, Mr Doherty said he had "no idea".
"I don't know about the IRA. But it won't go on forever," he said.
Three SDLP MPs are due to be sworn in at Westminster this week. South Down MP Eddie McGrady will be joined by party leader Mark Durkan and deputy leader Alasdair McDonnell, who replace John Hume and Séamus Mallon.
A spokesman for the SDLP confirmed that the three MPs will take a "solemn affirmation", instead of an oath of allegiance, to Queen Elizabeth.
However, the spokesman said the MPs would take a "de Valerea-esque" approach to the process' which they regarded as an empty formula.
However, Mr Doherty criticised the SDLP members for taking their seats in the House of Commons and for taking the parliamentary affirmation.
He said he, as an Irish republican, could not "swear any allegiance to any foreign monarch".
"We are serious about Irish unity," he said. "The focus must be kept on Ireland." Lady Sylvia Hermon, the sole returning Ulster Unionist MP was also at Westminster for the first day of the new parliament, claiming that the DUP vote had peaked.
She told The Irish Times that thorough and radical reform of her party was now essential to prevent it becoming irrelevant.
"Unless we change, and change is difficult when there isn't a safety net - unless we change we as a party are dead in the water." She warned colleagues against adopting a more hardline position in order to challenge Dr Paisley.
"If we try to move on to DUP territory, they will gobble us up and spit us out. You cannot outdo the DUP." Lady Hermon refused to be drawn on the question of putting herself forward as the next party leader and admitted she was torn between loyalty to her party and to her family including her husband, Sir Jack Hermon (78), who suffers from Alzheimer's disease.
Major reform of local government is likely when the next election is held in 2010. The Review of Public Administration, launched by the Executive in 2002, has suggested streamlining local councils with various combinations of 15, 11, or seven councils.