A potentially acrimonious Westminster by-election triggered by Barry McElduff's resignation as West Tyrone MP could delay plans for a fresh round talks aimed at restoring devolution.
The Northern Ireland Office was last night playing down the prospects that negotiations may be put on hold in the wake of Mr McElduff's decision to quit.
The Sinn Féin MP announced his surprise resignation via video yesterday morning, one week after being suspended by his party for three months.
The party's sanction, which saw the West Tyrone representative continue to receive a full salary and work out of his constituency office in Omagh, had been widely criticised for being too lenient.
The Co Tyrone man's apparently unilateral decision to fall on his sword came less than 24 hours after a moving interview on RTÉ Radio with Alan Black, the sole survivor of the 1976 Kingsmill massacre.
Mr McElduff caused outrage when he posted a video on social media on January 5 in which he placed a Kingsmill loaf of bread on his head.
The former MP insists he did not intend to cause hurt, but his tweet coincided with the 42nd anniversary of the atrocity in which 10 Protestant workmen died.
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Announcing his decision to quit, Mr McElduff said his greatest regret was the "deep and unnecessary hurt" his video had caused the Kingsmill families.
He again said any reference to the "terrible atrocity" in south Armagh had been inadvertent.
"I again offer my profound apology to those families and to the wider victims community," he said.
"Had I been conscious of the connection to the terrible atrocity at Kingsmill I would certainly not have posted that tweet. I genuinely did not make that connection, not for a second did I make that connection in my mind."
He described Kingsmill was "wrong, unjustifiable and sectarian".
"It should never have happened," he said.
The former MP and MLA added that he was saddened to be tendering his resignation after 30 years as a Sinn Fein member and public representative.
Mr Black welcomed the resignation.
"This past week has been truly awful for me. I am just hanging by a thread," he told the Press Association.
"But I am glad he has done the right thing."
Sinn Féin Stormont leader Michelle O'Neill said Mr McElduff had resigned because of the "unintended hurt" he had caused.
"Barry recognises that this controversy and his continuing role in public office is compounding the distress to the victims of Kingsmill, and again offers his profound apology to those families and to the wider victims community," she said.
"He has said that he does not want to be a barrier to reconciliation and I respect that decision."
DUP leader Arlene Foster said Mr McElduff had done the "right" thing but criticised Sinn Féin.
"He was not fit for public office and should have resigned in the immediate aftermath of posting the disgraceful video mocking and insulting the horrific terrorist events at Kingsmill," she said.
"Over the course of the last 10 days, Sinn Féin has failed to deal with the McElduff situation – by merely suspending him and continuing to pay him they compounded his disgraceful actions and demonstrated a lack of respect and compassion for the victims of Kingmill and indeed victims more widely."
The former first minister said republicans needed to "learn the lessons from these dark events".
SDLP leader Colum Eastwood said Mr McElduff's actions had caused "huge offence and immense hurt".
He referenced the RTÉ interview with Mr Black and said it was regrettable that had taken a week for Mr McElduff to "do the right thing".
“Many will welcome Mr McElduff’s resignation but will also question the failure of the Sinn Féin leadership to deal decisively with this issue," the Foyle MLA said.
Ulster Unionist Party leader Robin Swann also said the resignation should have happened last week.
"His position was absolutely untenable given the hurt and pain inflicted on the Kingsmill victims` families and the sole survivor Alan Black – this has been a horrendous experience for them," he said.
Green leader Steven Agnew said he hoped the resignation would bring an end to the episode.
"All this furore has achieved is to cause further upset to the families and I hope this resignation will now draw a line under it," he said.
But with early March earmarked as the mostly likely time for the West Tyrone by-election, an acrimonious campaign could jeopardise new Secretary of State Karen Bradley's efforts to re-start the Stormont talks.
A British government spokesman said the restoration of devolution was the secretary of state's priority.
"Progress has been made in talks between the DUP and Sinn Féin and the secretary of state believes that there is the basis for a deal," the spokesman said.
"The UK government's priority, as indicated by the secretary of state last week, is to reinvigorate talks with a short, intense push to restore devolution in Northern Ireland."
Barry McElduff announces his resignation:
