Labour Party leader Brendan Howlin has said the Brexit position of Britain's government amounted to "a very British coup".
Mr Howlin said he believed the British government does not have the support of its parliament for its Brexit strategy.
He also called for prime minister Theresa May to demonstrate her mandate for her position on the issue.
“It is entirely unclear that the positions being pursued by the British government have the support from the British parliament. What evidence we have suggests not. It appears too that the British government thinks so too. Having been defeated 15 times in the House of Lords the British government is yet to bring the EU Withdrawal Bill to the House of Commons ,” Mr Howlin said.
Mr Howlin, who is also Labour spokesman on foreign affairs and Northern Ireland, made the remarks in a statement issued on Saturday.
His comments come amid ongoing ridicule of a proposal from Britain's Brexit secretary David Davis to create a 16km buffer zone around the Border following Brexit.
Mr Davis's latest plan would give Northern Ireland joint UK and EU status so it could trade freely with both, as well as a buffer zone to eliminate the need for Border checkpoints with the Republic.
The proposals were roundly dismissed by Irish Government figures, members of the British parliament and the DUP, which urged the Tories to stop coming up with “half-cooked ideas” on how to deal with the Border question.
Pro-EU MPs have accused the British government of “making it up as they go along” when it comes to the issue.
Tory fears
“The May government is refusing to advance its own Trade and Customs Bill in the House of Commons . . . because it fears defeat at the hands of Conservative rebels and Labour, the SNP and the Liberal Democrats,” Mr Howlin said.
“Meanwhile, the EU is obliged to engage with a British government whose extreme Brexit position draws no mandate either from the people in the referendum or Westminster.
“With the key [European Council] summit coming up in the next month, I see no way whereby Ireland can assent to progress on talks. It is time for Britain and its parliament to get its act together.
“If Ms May has a mandate for her position, let her prove it. Ireland has suffered once too often at the hands of internal Conservative Party machinations,” Mr Howlin said.
