Democratic Unionists have been boosted ahead of the general election after UK Unionist leader Robert McCartney confirmed he will not be standing for the North Down seat which he held between 1995 and 2001.
Mr McCartney said he had been swayed by a commitment in the DUP manifesto that it would reject power sharing with Sinn Féin at Stormont.
His decision clears the way for DUP Assembly member Peter Weir to launch a vigorous assault on Lady Sylvia Hermon's seat in North Down and make it a tighter contest.
Mr McCartney, however, insisted he would continue to serve his constituents as an Assembly member for North Down.
The UKUP leader said: "After a great deal of heart-searching, I have decided not to stand for election in the North Down constituency.
"Now that the Democratic Unionist Party is about to confirm in its manifesto that `inclusive mandatory coalition government which includes Sinn Fein under d'Hondt or any other system is out of the question', I can conclude that the Belfast Agreement is finally dead and my main political objective has been achieved.
"To all those loyal supporters in North Down who have given me their encouragement and votes, I give my sincere thanks.
"I will continue to serve their interests and that of the pro-Union community in Northern Ireland as an elected representative and to `blow the whistle' when necessary if their interests or welfare are put at risk by those who may represent them in the future."
Mr McCartney's decision to clear the way for Mr Weir, a former Ulster Unionist who defected to the Reverend Ian Paisley's party in April 2002, also follows hard on two elder statesmen in the UUP appearing in election literature endorsing the Democratic Unionists' South Belfast candidate Jimmy Spratt.
Lady Sylvia Hermon captured the North Down seat for the UUP from Mr McCartney with a 7,324 majority over him in the 2001 General Election.
Her vote was boosted by the cross-community Alliance Party's decision not to field a candidate while the DUP also gave Mr McCartney a clear run.
However, Alliance have selected former Belfast Lord Mayor David Alderdice to contest the seat this time.
In the 2003 contest, the DUP spectacularly captured two Assembly seats and overtook Mr McCartney's party in North Down.
The Ulster Unionists remained the largest party in the constituency with 9,887 votes, with the DUP 2,642 votes behind, and the UK Unionists third largest party on 3,583.
Alliance had 2,655 votes but the fate of the seat could very much depend on Lady Sylvia's ability to mop up pro-Good Friday Agreement votes from parties like Alliance, the cross-community Women's Coalition and the Greens and independents.
Four independent candidates collectively polled 2,964 in the Assembly contest, although some were anti-Good Friday Agreement.
-PA