David Cameron's electoral project in Northern Ireland was under renewed pressure tonight after the Conservative Party failed to come good on a pledge to run in every constituency in the region.
The decision of the Tories' partners, the Ulster Unionists (UUP), to stand aside in Fermanagh and South Tyrone in favour of an independent candidate torpedoed Mr Cameron's promise to stand in all 18 seats.
In backing the UUP's controversial pact with the Democratic Unionists (DUP) that will see a non-affiliated "unionist unity" candidate running, the Conservatives have also been criticised for supporting a deal branded a "sectarian headcount" by nationalists and republicans.
The UUP and DUP have agreed to withdraw from the contest and back joint candidate Rodney Connor in order to maximise the chances of displacing sitting abstentionist Sinn Fein MP Michelle Gildernew.
But the move has been heavily criticised by Mrs Gildernew, the nationalist SDLP and a Tory architect of the UUP alliance who left the party in protest today.
"The unionist parties have cobbled together a regressive deal based on a negative agenda," said Mrs Gildernew.
"It is about base sectarianism, and the old agenda of division and inequality."
SDLP leader Margaret Ritchie was particularly critical of the Tories' stance.
"A so-called 'unity' candidate in Fermanagh South Tyrone is a gross insult to the people of that constituency," she said.
"David Cameron is guilty of propping up sectarian politics and reinforcing sectarian division."
Mr Connor, a former chief executive of Fermanagh District Council, said he would be prepared to accept the Tory whip at Westminster but insisted that in regard to local matters he would vote in the best interest of the region.
The Ulster Conservatives and Unionists New Force (UCUNF) has already suffered a number of blows since its creation two years ago, with a series of UUP members having resigned over the decision to align with the Tories, the most high profile being sitting North Down MP Lady Sylvia Hermon.
And today a Conservative who helped forge the original pact - former party vice chair in Northern Ireland Jeffrey Peel - left the Tories in opposition over developments in Fermanagh and South Tyrone.
"In effect the Conservatives are agreeing to yet another sectarian head-count to secure a candidate who will, sometimes, take the Conservative whip," he said.
"For me I have reached the end of the road and will now be tendering my resignation from a political party that has walked away from any sense of decency and honour in its pursuit of power.
"This is a very sad day for Northern Ireland. If the Conservative Party could stoop this low here it really begs the question whether the party is fit to govern the United Kingdom."
But Owen Patterson, shadow secretary of state for Northern Ireland, defended Mr Connor's candidacy, insisting he would attract support from all sides of the community.
Mr Patterson also made clear the Conservative Party had not been involved in negotiations with the DUP.
And in regard to the Tory pledge to stand in all 18 seats, he said the constituency was a special case.
"We recognise that Fermanagh and South Tyrone has characteristics that are unique within the UK," he said.
"It has been without any democratic representation for the past nine years. It is the one constituency where there is currently an abstentionist MP, where a single cross-community candidate could lead to the restoration of democratic representation at Westminster.
"In recent weeks and months there has been an upsurge of public opinion across Fermanagh and South Tyrone to find such a candidate.
"Rodney Connor has impeccable cross-community credentials and has a first-rate record of public service going back many years. He is hugely respected and admired on all sides.
"We therefore respect the decision of our Ulster Unionist colleague in Fermanagh to stand aside in his favour."
Earlier, Mr Connor insisted he would be a voice for all the people of Fermanagh and South Tyrone at Westminster.
"Through my work, over the years, I believe that I have already demonstrated a proven track record of delivering in the constituency for people from right across the community," he said.
"I know what Fermanagh and South Tyrone needs and I believe that I am well equipped to help deliver it."
Ulster Unionist MLA Tom Elliott, who stood aside in favour of Mr Connor, rejected the allegations of sectarianism.
"We must ensure that this opportunity is not lost to the community and provide representation at Westminster for the people of this constituency instead of an abstentionist MP," he added.
DUP economy minister Arlene Foster, who had been due to run for her party in the constituency, said she was delighted Mr Connor would be standing as an agreed candidate.
"When unionism is divided, unionism is weakened," she said.
"I have no doubt that Fermanagh and South Tyrone can set the example for other areas in Northern Ireland to follow."
While the DUP and UUP reached agreement in Fermanagh and South Tyrone, talks to find a single candidate in another marginal nationalist seat - South Belfast - have thus far come to nothing.
Mr Patterson dismissed talks of another localised deal at the expense of a UCUNF candidate.
"There is no desire to have any such arrangement elsewhere," he said.