Sinn Fein has refused to acknowledge Westminster's jurisdiction over Ireland since it was founded in 1905, which means that its candidates stand on an abstentionist ticket.
This has not stopped republicans from mounting vigorous election campaigns at Westminster elections, both before and after the partition of Ireland in the 1920s.
Sinn Fein notched up its greatest success in the 1918 general election - the last before partition - when it won a massive majority of the vote in Ireland. The IRA has claimed its right to take up arms against Britain from Sinn Fein's success in what was the last all-Irish election.
Republicans also scored a historic first in 1918 when Countess Markiewicz, of the Anglo-Irish Gore-Booth family, became the first woman to be elected to Westminster. She refused to take her seat.
After the partition of Ireland, Sinn Fein became so divorced from the political process - its leader Eamon de Valera set up Fianna Fail in 1927 - that it also boycotted the Irish parliament. Pure republicans in Sinn Fein claimed that the Dail was almost as illegitimate as Westminster because it only covered 26 of Ireland's 32 counties.
Sinn Fein refused to take its seats in the Dail until 1986 when Gerry Adams and Martin McGuinness overturned the party's abstentionist policy at an acrimonious ard fheis, or party conference. Their historic move, which only succeeded after a passionate speech by Mr McGuinness, split the party and led its former leader Ruairi O Bradaigh to set up the rival Republican Sinn Fein.
Sinn Fein had to wait until 1997 to see its first TD (MP) in the Dail since de Valera walked out after partition in 1922. Caoimhghin O Caolain was elected in the border seat of Cavan-Monaghan, opening up the prospect of Sinn Fein holding the balance of power in Dublin if it secures another three seats at the next general election.
Across the border in Northern Ireland, Sinn Fein watered down its boycott of Westminster when the party stood on a ticket of "active abstentionism" at the 1997 Westminster election. Under the new policy Gerry Adams, who was elected as MP for West Belfast, and Martin McGuinness, who was elected as MP for Mid Ulster, pledged to use every facility at Westminster short of taking their seats in the chamber.
Despite the party's move towards constitutional politics, there is still no appetite to swear the oath of allegiance to the Queen. If the government removes the reference to the Queen from the oath, which would bring it into line with the one sworn in the Northern Ireland assemby, then Sinn Fein MPs could be seen in the chamber.
Arthur Griffiths, who founded Sinn Fein in 1905, may have taken a more relaxed view. He was a "dual monarchist" who believed that separate monarchs should govern Britain and Ireland.
