By David Young
Sinn Fein's political rivals have claimed its Westminster abstentionist policy has dealt a damaging blow to Ireland by handing Commons victories to hardline Brexiteers.
The two biggest parties in the Irish Republic - Fine Gael and Fianna Fail - and the SDLP in Northern Ireland are among those blaming the republican MPs for the outcome of Monday night's razor-edge votes on the UK Government's Customs Bill.
They claim amendments secured by Brexiteers undermine agreements between the UK and EU aimed at avoiding a hard border in Ireland post-Brexit.
Sinn Fein has seven MPs at Westminster. None of them take their seats due to the party's century-old policy of abstentionism.
At last year's general election, three pro-Remain SDLP MPs - Mark Durkan, Alastair McDonnell and Margaret Ritchie - all lost their seats.
In Northern Ireland, 56% of the electorate voted to Remain. However, in Westminster 10 of the 11 MPs from the region who take their seats are Democratic Unionist Brexiteers.
Sinn Fein has dismissed the criticism about not taking its seats, insisting its MPs were specifically elected on an abstentionist policy, indicating that the republican/nationalist community in Northern Ireland reject Westminster politics.
The republican party has accused its rivals of trying to score cheap political points on the issue.
Micheal Martin, leader of main opposition party Fianna Fail, tweeted on Tuesday morning: "Hardline Brexiteers won last evening's Westminster vote because of Sinn Fein abstentionism.
"Anti-Brexit majority in Northern Ireland not represented in any forum. Durkan, Ritchie and McDonnell would have defeated that damaging vote for Ireland."
In the wake of the votes on Monday night, Ireland's justice minister, Fine Gael's Charlie Flanagan, also pointed the finger of blame at Sinn Fein.
He tweeted: "The refusal by Sinn Fein to take up its Westminster seats has plunged the British PM in to the clutches of the hard Brexiteers again. Government wins knife edge vote by wafer thin margin. #Brexit."
SDLP leader Colum Eastwood tweeted: "To those who say Westminster doesn't matter - wake up. Our future is being torn apart by the British Government. Abstentionism is not acceptable. Sinn Fein gift Theresa May a win over Brexit. SDLP MPs would have been there to stop Tories."
Sinn Fein senator Niall O Donnghaile responded to Mr Eastwood's tweet in robust terms.
He tweeted: "Wake up. Nationalism has turned its back on Westminster. Wake up. Every nationalist constituency in the North elected an abstentionist MP. Wake up. Nationalism looks to Dublin (where the SDLP abstain from politics) for their
political futures. Wake up."
One of Monday night's amendments - the insertion of a legal guarantee that there will be no post-Brexit customs border between Northern Ireland and Great Britain - appears to undermine the terms of the co-called "backstop" position agreed by the UK and EU last year, which stated that Northern Ireland would remain subject to an EU customs regime if a wider trade deal failed to materialise.
While Prime Minister Theresa May had already rejected suggestions that there could be a customs border between Northern Ireland and the rest of the UK, many Remainers believe the legally binding amendment has reduced the chances of securing an agreed backstop in the withdrawal treaty.
That amendment was passed without a vote in the Commons on Monday; however, another amendment that could have implications for the backstop - that the whole of the UK will leave the EU's VAT regime - was only passed with a majority of three.
A further amendment that was also passed by just three votes - preventing the UK from collecting tariffs on behalf of the EU unless the rest of the EU reciprocates - has, Remainers contend, also increased the prospect of a no deal Brexit.
DUP MP Sammy Wilson said the outcome of the Westminster votes had strengthened the UK's hand in the Brexit negotiations.
"The DUP were proud to be able to deliver their support in two crucial votes in the House of Commons last night," he said. "Votes which will ensure the United Kingdom will have a stronger hand in negotiations with the EU."
Mr Wilson said the outcome had secured Northern Ireland's part in the United Kingdom.
In a reference to Remain politicians in Northern Ireland, he added: "The irrational rage against safeguards which will now be included in legislation is due to their blind opposition to anything proposed by those who wish to leave the EU."