Houses of Parliament, London: The Commons is divided into a large number of factions from hardcore Brexiters who want a no deal exit to hardcore remainers. Photograph: Dominic Lipinski/PA Wire

European Union leaders gave Prime Minister Theresa May assurances on Thursday (December 13) that they would seek to agree a new deal with Britain by 2021 so that the contentious Irish 'backstop' is never triggered.

As the clock ticks down towards Brexit day in March and with political chaos still reigning in London, politicians in Dublin are becoming understandably nervous.

On one level, Ireland has enjoyed perhaps its greatest ever diplomatic success: the entire EU has placed its negotiating weight on the line to ensure that Brexit does not result in a hardening of the Irish border.

However, on the other hand the backstop that the EU pressured Theresa May to accept has provoked so far insurmountable opposition in the House of Commons thus increasing the chances of the UK crashing out of the EU with no deal.

As an Irish diplomat was quoted as telling the Bloomberg news agency, “this will either be an incredible diplomatic triumph or a strategic mistake”.

With the possibility of a hard economic border, economic chaos and poisoning of UK-Irish relations as results of Ireland’s backstop gamble backfiring, it is worth thinking about what needs to happen if this gamble is to come off.

The fundamental premise of the Irish Government’s approach has been that the British authorities will either swallow the backstop or cancel Brexit altogether to avoid the chaos of a no-deal Brexit.

This means that the current Withdrawal Agreement is currently miles off securing majority support. There will have to be a game-changing development at Westminster for the current agreement to get through. If there is no agreement between the UK and EU then, under EU law, a no-deal Brexit happens automatically in March. It is possible that Ms May will run down the clock and, faced with a choice between her agreement and no deal, MPs reluctantly vote it through - but relying on that happening is very risky proposition.

The UK can only validly revoke its notification of its intention to leave if it has definitively decided to stay in the EU The Irish Government’s approach could also result in triumph if the unattractive nature of a Brexit constrained by the backstop (the backstop leaves the UK constrained to follow EU laws in many areas without having a vote on those laws) causes the UK to abandon Brexit altogether.

This hope received a boost from the European Court of Justice ruling that held the UK was entitled to revoke its triggering of Article 50 and remain an EU member without the permission of the other member states.

Many prominent figures such as John Major have suggested that this ruling means the UK should cancel its notification of its intention to leave in order to gain time for reflection and debate. However, this is not legally possible.

The ruling of the court made it clear that any revocation of intention to leave has to be unequivocal and definitive. In other words, the UK can only validly revoke its notification of its intention to leave if it has definitively decided to stay in the EU. It cannot revoke in order to pause the process.

Time is running short to take such a momentous decision. While legally the British parliament could take the decision to overrule the Brexit referendum result, politically, abandoning Brexit would need another referendum.

Just because almost no one wants a no deal Brexit, does not mean that it will not come about A referendum cannot be organized and completed before the end of March. This means that, under Article 50 the UK would need the unanimous permission of the 27 Member States to postpone the day on which Brexit takes effect in order to allow a referendum to take place.

Sucking up Most Member State governments are tired of the Brexit process which they see as sucking up time and energy that could better be used to address the serious problems facing the EU.

It is not clear that all states would agree to extend time unless they were assured that the UK government would be recommending a remain vote. A Conservative Prime Minister to endorsing remain in a future referendum seems, at the moment, a remote prospect. Furthermore, there is no guarantee that remain would win a second referendum. The polls have not shifted very much since 2016.

In short, the current approach of the Irish Government may come off but it may not. There are very large political and legal obstacles in the way of either desired outcome (acceptance of the backstop or cancelling Brexit).

Just because almost no one wants a no deal Brexit, does not mean that it will not come about. Almost no one wanted a World War in 1914 but the parties ended up taking a series of individual decisions that ultimately led to a conflagration that was in no one’s interests. The Irish Government has bet heavily on the idea that the UK will not self harm. Looking at the chaos in London, that may not have been a wise bet.

Ronan McCrea is Professor of Constitutional and European Law at University College London