Brexit has changed the conversation around a united Ireland, Sinn Fein MPs said Wednesday as the Irish republican party urged Dublin to prepare for a referendum. The debate around how the currently-invisible border between Northern Ireland -- part of the UK -- and the Republic of Ireland would operate after Brexit have proved the stickiest part of negotiations for Britain to leave the European Union. Sinn Fein's newly-elected Belfast North MP John Finucane said discussion around a border poll was now "mainstream". Speaking in London as Sinn Fein's seven MPs met outside the Houses of Parliament while lawmakers returned to the legislature, he said the Brexit vote in 2016 "changed forever the conversation around a new Ireland". "It needs to be a very well-informed and reasoned debate and for that we need the Irish government to step up." The UK is due to leave the European Union on January 31. While 52 percent across the UK as a whole voted for the kingdom to leave the EU, within Northern Ireland, 56 percent wanted the UK to stay in the bloc. Sinn Fein are the biggest party representing the Catholic community in Northern Ireland. Its MPs do not take their seats in the British parliament as they refuse to recognise its jurisdiction over Northern Ireland or swear allegiance to Britain's head of state, Queen Elizabeth II. "We are here to raise the issue of Irish unity," said West Belfast MP Paul Maskey. The island of Ireland was partitioned in the early 1920s, with six northern counties -- then heavily populated by pro-British Protestant unionists -- opting to stay within the United Kingdom while the rest of Ireland left. The Irish constitution says a united Ireland can only be brought about with democratically-expressed majority consent in both jurisdictions. British laws say a poll can be called in the province if the government's Northern Ireland secretary feels it likely that a majority would vote to leave. Meanwhile talks are ongoing in Belfast on restoring the devolved Northern Ireland Assembly, which collapsed in January 2017 due to a breakdown in trust. Northern Ireland has been run by civil servants since then. If a deal is not reached by the Monday deadline, legislation to give civil servants additional powers to run the province's struggling public services expires and fresh elections are due to be called. rjm/klm