Theresa May stressed the importance of the Union of England, Scotland, Wales and Northern Ireland in her Brexit plan speech at Lancaster House. Indeed, whether by deliberate choice or casual co-incidence she dressed in a Scottish tartan trouser suit while revealing her long-awaited vision of Britain’s future after EU membership ends.

The government’s much anticipated stance on the single European market was given pride of place in May’s speech. Less certain in her articulation were the choices the country will ultimately face: future trade with the EU, and the impact on businesses, jobs and living standards.

Central to everything the prime minister said was the following assumption, based, presumably, on careful political calculation: that the union of the constituent parts of the United Kingdom would hold together, bound inexorably by the challenges now facing the entire nation.

Whether this represents a political gamble that backfires, only time will tell. Scotland faces a political quandary, Northern Ireland faces a political vacuum and the welsh government cannot protest too strongly about the United Kingdom’s self-removal from the single market, given that the people of Wales voted to leave the EU in June last year.

What this also represents is a profound shift in the conventions of UK public policy-making. Theresa May’s speech yesterday marks the break-up, at least in terms of policy-making by consensus, in parliament and the devolved administrations.

The prime minister established the meetings of the Joint Ministerial Committee (JMC) to bring together the political leadership of England, Scotland, Wales and Northern Ireland. It has met infrequently and the joint communiqués, issued by the Department for Exiting the European Union reveal very little detail about the tone or level of debate during these meetings.

This committee is the only formal mechanism by which the nations and regions of the United Kingdom can reach some form of joint strategy for the forthcoming negotiations with the other twenty-seven EU member states. It is clear from the interviews given by Nicola Sturgeon and Carwyn Jones that neither of these first ministers had any advance indication of the blunt messages the prime minister delivered in her speech. Arlene Foster, first minister in Northern Ireland is otherwise distracted by the aftermath of the Cash for Ash scandal and the imminent crisis elections on the 2nd of March.

It is almost impossible to ignore the politics of Brexit in considering the implications of Brexit on the policy-making processes that shape the relationship between the United Kingdom and the wider-world. Foreign policy development does not operate in a political vacuum. Equally, it is difficult to ignore the underlying political calculation in May’s 12 point Brexit plan – she leads a government with a small majority of 14 MPs in the House of Commons.

The natural ebb and flow of the parliamentary sessions results, almost inevitably, in reducing government majorities even further. Perhaps the most apt comparison, at this stage, is between the Callaghan Labour government of 1976-1979 when a single-figure majority was reduced to the point where the government could not survive and an election followed, resulting in the Thatcher governments from 1979-1990. It is, therefore, not unreasonable to expect a prime minister, contemplating the potential need to secure an increased majority at the polls – perhaps before 2020 – to place political expediency above the need for calm, measured discussion with the devolved administrations of the union. Given the level of secrecy required for Whitehall to conduct its preparations, for the start of the tough discussions with the EU that the government faces in a matter of weeks, the JMC can be seen as little more than window dressing on the state of the union.

The longer-term consequences for the integrity of what binds the four constituent parts of the United Kingdom together, are unknown. It is not fanciful to imagine that public resentment in Scotland, that the popular will of the people is being deliberately ignored by Westminster – specifically, the conservative government – will lead, ultimately, to a second independence referendum. In Northern Ireland, despite the current political turmoil, a similar resentment could manifest itself when the prospect of a ‘hard border’ with the Republic of Ireland starts to loom large as the UK prepares to leave the EU. May has placed great trust in the European Union recognising that the continued benefits of relative peace in Northern Ireland require a special arrangement to negate the need for a physical border between this part of the UK and Éire. There is no guarantee that leaders of the EU27 will agree to this.

The only certainty inherent in the government’s approach to Brexit is that it has abandoned any pretence that it wants to reach a consensus between England, Scotland, Wales and Northern Ireland, in its policy-making approach to Brexit. Clearly, in the case of Scotland, the prime minister has concluded that the first minister’s stated aim of keeping Scotland in the single market is completely incompatible with her own judgement that membership of the single market and customs union, for the UK, represents continued EU membership by ‘the back door’.

The devolution arrangements, particularly for Scotland and Westminster, have enabled politicians of different parties to coexist as separate but intertwined representatives of the people in delivering budgetary and practicable policy implementation of UK-wide policies. Devolved policy-making – that is policies designed, developed and implemented in Scotland, Wales and Northern Ireland, were seen as a separate political and administrative necessity by Westminster.

May’s speech yesterday could change this peaceful coexistence forever. Policy-making authority is being challenged. What right does Scotland have to try and influence UK national policy for Europe, especially after a UK-wide referendum requires the government in Westminster to carry out the instructions of the voters? What right does a conservative government, essentially representing only England and Wales, have in taking Scotland out of the single market and the European Union, when the people of Scotland voted overwhelmingly against this? What right does the government in London have in leading a process that results in citizens of Northern Ireland requiring passports to travel between Belfast and Dublin. These are profound political questions but they are also profound questions of principle in the policy-making processes that have served the union since the reign of Queen Victoria.

These questions will be at the heart of the discussions that lead to the final UK withdrawal agreement to be signed by Theresa May and her counterparts in the European Union.

If the implications inherent in these questions are not fully considered, and an amicable solution reached by consensus, the long-term future of national – United Kingdom – policy-making process could be at risk. Inevitably, this could have political and social consequences for the future of the union itself.

It will only be at the time of the vote in parliament, on the terms of the final withdrawal agreement, that we will know whether the prime minister’s speech represented a reckless gamble or visionary leadership.