The decision to resort to a referendum to decide on the UK’s EU membership was always going to lead to difficulties. The bitter divisions it opened up undermined two key features of the UK’s constitution. First, it undermined the organising principle of the British constitution; the idea of parliamentary sovereignty which has traditionally meant that parliament is the ultimate decision-maker on all matters.
The referendum moved parliament from its role of taking decisions to the role of implementing the electorate’s decision to leave the EU, no matter how vague and confused the instruction given by voters.
As importantly, Brexit has undermined the role of what are called "constitutional conventions".
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These conventions are a set of expectations shared by key political and legal actors about how things ought to be done. They are very important in the British system because the constitution is uncodified, so there is no single written text to refer to in order to decide constitutional questions.
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Indeed, conventions can be so powerful that they can turn the situation in practice into the opposite of the situation on paper. For example, on paper the queen can veto any legislation she does not approve of, but by convention she always signs legislation that has been passed by parliament.
Because these conventions consist of shared expectations rather than strict legal rules, they have come under great strain in an era of rancorous political conflict, where each side feels the stakes are sufficiently high to justify breaking with established ways of doing things.
Thus, earlier in the year we saw actions such as the speaker of the House of Commons (who is sympathetic to remaining in the EU) abandoning the long-standing precedent that gives the government control of the timetable of the House of Commons. Then on Monday, to the fury of the government, he intervened again, citing a controversial principle of parliamentary procedure to prevent the government from seeking a third vote on the May deal.
Pressure
The hyper-partisan atmosphere of Brexit has even placed pressure on the non-partisan status of the queen as a debate has emerged as to whether she ought to refuse to sign Brexit-related legislation passed by parliament against the wishes of her government.
Most importantly, the key assumption of the British system that the government controls the Commons, and is, therefore, capable of taking key political decisions, has been destroyed.
May’s Brexit policy, the central policy of her administration, has now been defeated by hundreds of votes in the Commons not once but twice.
In any normal circumstances this would cause the resignation of the government. Yet with major divisions in both Labour and the Conservatives on Europe and intense dislike of Jeremy Corbyn by conservative rebels, the failure of May’s central policy has not caused her government to fall.
The result has been political paralysis. May’s administration is in office, but is manifestly incapable of taking decisions on the key issue facing the UK.
This is a highly frustrating situation for the UK’s negotiating partners. The EU has been clear that this deal, as clarified last week in Strasbourg, is its final offer.
Even if it were willing to talk further, with whom could it negotiate? There is little point in negotiating with a prime minister whose policies have been rejected by a huge majority in parliament.
This political paralysis in London is highly dangerous as the structure of article 50 means that the default position remains the UK crashing out on March 29th if no deal has been agreed.
While a short extension to article 50 may be granted, any extension beyond a few months is legally very difficult.
The EU is keenly aware that if Britain is still a member state by the time the new European Parliament meets in July, this could place the validity of that parliament in doubt.
Long extension
In addition, many in the EU are wary of granting the UK a long extension which could mean the UK threatening to wield its veto in areas such as the EU budget unless it is granted further concessions on Brexit.
We could well end up in Ireland’s ideal situation where the backstop ends up acting as the agent that revealed Brexit’s internal contradictions and resulted in the cancelling of the whole project.
However, we could also end up in a situation where the UK’s inability to swallow the backstop produces paralysis and ultimately a chaotic Brexit, with the hardest of borders north-south and east-west.
Either way it is now clear that Britain’s uncodified constitution cannot cope with referendum democracy. Indeed, even if Brexit is ultimately cancelled the hyper-partisan politics it has brought about may make the UK constitution unworkable in the long term.
Ronan McCrea is professor of constitutional and European Law at University College London