Half-informed American here so I apologize if this seems like a naive question on British politics.

Given the strong preference of many in Ireland to avoid a hard border between the Republic of Ireland and the UK, would the votes of the Sinn Fein make any difference in the outcomes of these very narrow votes in Parliament?

Of course any single vote could swing something; I am asking are the votes close enough on these issues that seven votes would make a difference on a resolution that the Sinn Fein would care about.

(I appreciate that taking a seat in Parliament would involve taking oath. I thought that the stakes might make it worthwhile.)

Edit update: I am not asking if they would vote for or against the current government and I appreciate participation in Parliament would rankle an SF member. However, if that participation could make the difference in a decision that will (1) have consequences for decades to come and (2) have an effect on both NI and the Republic of Ireland - could they and would they make a difference?


4 Answers 4


Sinn Fein's purpose is a united Ireland. They don't regard British rule over Northern Ireland as legitimate, and swearing the Oath of Allegiance would be anathema to them. They'd be no more willing to do it than members of ISIS would be to swear allegiance to the USA. They are very serious about their motives, and do not want to be seen as cynical politicians.

They have no reason to support the May Deal. A no-deal Brexit would enable them to blame the effects on Northern Ireland on the British and the DUP, which could incline some of the population of NI towards voting for Sinn Fein and a united Ireland.

Addendum, May 2022: The objective of getting the population of NI to vote for Sinn Fein is making progress. The first major election in Northern Ireland since Brexit has now taken place. The DUP, which was strongly in favour of Brexit, has lost three seats in the Northern Ireland Assembly (that's a huge shift in this tribalized political environment), making Sinn Fein the largest party for the first time. The Alliance Party, which was opposed to Brexit, has gained 9 seats (up from 8 to 17). Sinn Fein would seem to be making progress towards a peaceful transition to a united Ireland.

No, Sinn Fein have not taken their seats in the UK Parliament. Their reasons for that remain the same as ever.

  • 1
    Exactly this. SF voting in the UK parliament would be such a Pyrrhic victory that it could destroy the party from the sense of betrayal (even if they had some position or other on Brexit). Sinn Fein stand for the UK parliament on a ticket of illegitimacy of that election.
    – Dan
    Mar 18, 2019 at 9:03
  • 4
    Indeed, if they are going to ever take their seats, it would be as part of an overall shift of principles/ stratagy, not a one-off vote that is not so clearly in their interests
    – user19831
    Mar 18, 2019 at 10:43
  • 1
    Sinn Féin support the Withdrawal Agreement. They consider themselves an Irish party, and for the UK to leave without a deal would be very bad for Ireland, united or not. However, they support it from their perspective of a foreign observer.
    – gerrit
    Mar 19, 2019 at 16:31
  • Regarding the addendum: what exactly has worked? Does Sinn Fein now hold seats in the UK Parliament? May 8, 2022 at 14:42
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    @Trilarion: Better now? May 8, 2022 at 16:01

There have been a few close votes over the last couple of years on Brexit. Most recently, Sinn Fein might plausibly have voted last week to give Parliament control over Commons business to hold indicative votes on what forms of Brexit deal could command a majority. That amendment was lost by 2 votes so Sinn Fein would easily have swung it:


  • 3
    Upvoted for being the only answer of three (at time of writing) to actually attempt to answer the question.
    – Darren
    Mar 18, 2019 at 5:31
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    @Darren This SE is about politics, not arithmetic. Politically, the arithmetical answer is completely hypothetical.
    – alephzero
    Mar 18, 2019 at 11:28

For all I know, Sinn Fein could take seven seats in the UK parliament, but they don't. I think the background is that to become an MP, you have to swear your support for the UK or something like that, and they just won't do that. No chance. Not going to happen. Ever. So Sinn Fein could vote in the UK parliament, but they never, ever will.

(Admittedly, never is a very long time)

  • 2
    I suppose that Sinn Fein's members would be more than happy to support the UK as a neighboring foreign sovereign power. What they won't do is swear their allegiance to the UK or, more precisely, to the queen.
    – phoog
    Mar 19, 2019 at 12:58
  • @phoog In the unlikely event that the UK would become the UR, SF would still not take their seats...
    – gerrit
    Mar 19, 2019 at 16:34
  • @gerrit of course. In that case, there would still very likely be an oath of allegiance to the republic or the constitution or some such, but the oath is symbolic and the real stumbling block would be participating in the government that they regard as illegitimate. My point was not so much about whom the allegiance is owed to as about the difference between allegiance and support.
    – phoog
    Mar 19, 2019 at 17:13

As other answers have said, they can blame the repercussions of Brexit on the British which suits them and they have never been willing to take the oath.

Other answers miss that they are elected on an abstentionist ticket, they have promised their constituents that they will not take their seats and doing so would break that and lose them votes.

Additionally, were they to ever do it in a close enough vote for their votes to matter, there would be enough MPs that would swap sides just to spite them in an "anything the IRA want is bad" way.

Basically, taking their seats and getting involved in the petty party politics in Westminster doesn't in any way serve them or their constituents so they will never do it.

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