It’s fair to say that Northern Ireland isn’t exactly a trail blazer when it comes to social justice issues. Long after England, Scotland, Wales and finally the Republic of Ireland voted to legalise same-sex marriage, the country continues to lag behind.

However, this changed yesterday as Northern Ireland finally voted yes to same-sex marriage. A cause for celebration, you might think, but same-sex couples won’t be booking into registry offices any time soon. Despite the bill being supported by 50.5 per cent of MLAs, it still cannot pass due to the Democratic Unionist Party (DUP) blocking it.

This has happened because under the devolved Stormont parliament, political parties can trigger a “petition of concern” to block legislation in the chamber. Once issued, it means that a bill cannot just get a simple majority vote overall, instead it needs to get a majority amongst Nationalist or Catholic politicians, as well as a majority amongst Unionist or Protestant politicians.

Many of the DUP’s leading politicians are staunch traditional Protestants who are fierce in their opposition to what they term “sodomites” within Northern Ireland. They are resolute in their determination to block LGBT rights through any means possible, no matter how underhand or undemocratic.

Although they were unable to stop same-sex marriage being approved by a majority, the DUP were able to stop it from being approved by a majority of Unionists by triggering the petition and then voting no themselves. This technicality meant that today’s vote cannot count and Northern Ireland will remain the only part of the UK or Ireland without marriage equality.

The “petition of concern” mechanism is thought to be unique to Northern Ireland’s political structures and was embedded in power-sharing to protect either side of the religious divide if a bill was genuinely harmful or unjust towards either ‘side’. However, the DUP have begun misusing the process in order to block same-sex marriage in Northern Ireland.

Today’s vote leaves Northern Ireland in a difficult position in terms of democracy. It will have significant repercussions for the nature of devolution and the relationship between Westminster and Stormont.

Westminster will now have to consider whether to intervene to circumvent the DUP’s petition in order to enable Northern Irish same-sex couples to finally marry. If they do not do so, they will be accused of letting the DUP’s bully tactics triumph and of allowing the Northern Irish LGBT community to suffer.

Yet, if Westminster does intervene, it will also face accusations of undermining the principle of devolution- that Northern Irish issues are for Northern Irish politicians alone to deal with.

Above all, the incident is yet another example of how power sharing structures negotiated in the 1990s are showing their strain. Whilst they might have proved effective elements of the Assembly in its infancy, “petitions of concern” are being misused by politicians to undermine the business of their own parliament. As Stormont’s near collapse in September proved, a number of elements of the Good Friday Agreement and Northern Ireland Assembly are proving to no longer be fit for purpose and are doing more to impede than support democracy in the province.