Sinn Fein's four members of the United Kingdom parliament took up their offices at Westminster this afternoon but pledged to never sit in the Commons.
And while each MP will receive allowances of over stg£100,00, none of them will be paid as members of Parliament.
Its four elected MPs - Mr Gerry Adams, Mr Martin McGuinness, Mr Pat Doherty and Ms Michelle Gildernew - have refused to take the oath of allegiance to the British crown which all new MPs are required to swear.
"There will never, ever be Sinn Fein MPs sitting in the British Houses of Parliament," Mr Adams said.
"The transfer of power by London and Dublin to the assembly in the North ... is all proof of where we see the political centre of gravity on the island of Ireland, and that is in the island of Ireland."
"We are here, elected, with our mandate renewed and increased," he added.
The move has provoked an angry reaction from Unionists, who complain Sinn Fein has promised nothing in return for the concession of office space and annual expenses of €176,000 (Stg£110,000) for each MP.
Earlier Mr Adams met British Prime Minister Mr Tony Blair for talks and urged him to tackle the threat of loyalist paramilitaries.
AFP