By Harriet Line, Press Association Political Correspondent
Sinn Fein's refusal to take their seats in Westminster and voice their concerns over Brexit is a "tragedy", a former Irish prime minister has said.
John Bruton said the voice of Irish nationalism was missing in the debate over the UK's withdrawal from the EU, as he criticised the left-wing republican party's "extremely bad" record for not sitting in the Commons.
Sinn Fein refuses to take its seats out of opposition to Westminster's jurisdiction in Northern Ireland and the oath all MPs must make to the Queen.
Mr Bruton, a former Fine Gael politician who served as taoiseach from 1994 to 1997, told BBC Radio 4's Today programme: "I think the record of Sinn Fein MPs not taking their seats in Parliament has been extremely bad.
"Ireland was partitioned in 1920 when Sinn Fein refused to take their seats after the 1918 election.
"Sinn Fein have refused to take their seats on this occasion and the most serious threats to the position of Northern nationalists are now about to be realised - with no Sinn Fein, no Northern nationalist voice to argue a different case.
"I think it's a great shame, it's a tragedy."
He also said there would be a hard border between the Republic of Ireland and Northern Ireland if there is no agreement between the UK and the EU.
HE said: "There will be a hard border if there is no agreement - that's clear under EU law if you look at the paper that was produced last month by the European Commission - it's quite clear that there will have to be control on the EU's borders and one of those EU borders in the event that Britain leaves the EU will be in Ireland."
And he suggested those opposed to the controversial backstop proposals to avoid a hard border on the island of Ireland do not believe there would ever be an "acceptable agreement".
He told the programme: "One suspects that those who object to the backstop are people who don't really expect there ever will be an acceptable agreement that would avoid a hard border in Ireland or between Ireland and Britain."