In The Ultras, the brutal, brilliant novel by Eoin McNamee set during the Troubles, the protagonist (based on the real-life undercover British intelligence officer Robert Nairac) finds himself in the company of dangerous men like himself. The Ultras plot terrible events and create dark polities while forcing everyone else to live with their consequences. “Ultra meaning beyond,” wrote McNamee. “Ultra meaning extreme.”

The so-called war cabinet formed by the new British prime minister, Boris Johnson, and whose course the maverick arch-Brexiteer Dominic Cummings now charts, of course bears no resemblance to the characters in the war of the Ultras imagined by McNamee. But the sheer velocity and ferocity of their opening salvoes about crashing out of the EU with no deal on October 31 unless the backstop – the insurance policy to avoid a hard border in Ireland – is abolished, raise the kind of alarm that we in Ireland have not felt since the dark years of the Troubles.

'We should be afraid' - Irish PM Leo Varadkar steps up warning about no deal Brexit - live news Read more

The political fear is that this new breed of “Brexit Ultras” (Johnson’s cabinet with Nigel Farage’s Brexit party snapping at its heels) could deliberately pursue a no-deal EU exit at the expense of a volatile Irish peace.

The sabre-rattling and pre-emptive blame-shifting of course is intended to shore up political support in the UK ahead of a possible general election, but also to intimidate Ireland into abandoning the backstop while shaking the unity of the EU27. Europe, with its own demons to face, has its red lines too and will not sacrifice the single market or its external borders, or jeopardise the wider integrity of the European project. Ireland, and the fragile peace process that has been built over the past 20 years, falls between these two positions.

And while it is still early days for the Johnson premiership, we have a deteriorated state of Anglo-Irish relations following his ascent to power. How real is the damaging rhetoric emanating from London and the anti-Irish tropes spewing from much of the British media? David Yelland, the former editor of the Sun, revealed that he had been shocked when “Tories of influence” told him privately that Leo Varadkar, Ireland’s taoiseach “isn’t bright” and “the Irish will blink”. “It seems, amazingly, that this is the actual policy of HMG under Johnson,” tweeted Yelland. “They are anti-Irish, arrogant, dangerous and wrong.”

That relations between London and Dublin are now strained is beyond dispute, though officials in Dublin insist that much of the noise is to be expected and aimed at a domestic UK audience rather than Ireland or the EU.

Still, following his appointment, it took almost a week for Johnson to place a phone call with Varadkar, who leads a confidence-and-supply coalition that – while shaky on a series of domestic issues – serves as a national government in all but name for the purposes of Brexit. When the phone call did proceed, both men adopted an uncompromising stance: Johnson insisting the removal of the backstop is a precondition for any deal, Varadkar adamant that the EU will not relent on the withdrawal agreement.

Varadkar rightly reminded Johnson of the British government’s obligation – as a co-signatory of the Good Friday agreement – to exercise its power in respect of Northern Ireland with rigorous impartiality. Johnson’s government relies, for the time being, on the support in the Commons of the Democratic Unionist party to prop up its narrow majority. The difficult parliamentary arithmetic, combined with Johnson’s inflammatory rhetoric, represents a serious challenge to the UK’s obligation to act as an honest broker in respect of Northern Ireland – the majority of whose citizens voted, like their Scottish brethren, to stay in the EU.

Facebook Twitter Pinterest Irish taoiseach Leo Varadkar and UK prime minister Boris Johnson. Photograph: Rex and PA

And although unionists are being comforted, for now, by Johnson, their confidence that a hard Brexit will not give birth to a united Ireland must also be fraying at the seams. This is not least because nearly two-thirds of the Tory party indicate in polling that they would rather sacrifice the union – and see Northern Ireland and Scotland leave it – than abandon Brexit.

Johnson (just like his predecessors) has yet to offer any meaningful alternatives to the backstop, yet blindly insists, as a pre-condition to talks with Brussels, that it must be removed. Given such a hardline starting point, what compromises would a deal with Brussels before October 31 entail? The recent ITV interview with the foreign secretary Dominic Raab on the issue of what flexibility the UK government has shown to date does not augur well for what lies ahead.

The high-handed, perhaps not entirely unexpected tone of the hard Brexiteers, including Johnson, has undoubtedly reawakened bad memories in Ireland. Nobody on the island is blind to the reality that in standing by the backstop in order to avoid a hard border, they could end up with one if the UK crashes out without a deal. Indeed, the Irish government has conceded, in its latest updated contingency action plan, that it will implement increased checks and procedures in the event of a no-deal Brexit. That means border infrastructure and checkpoints that, however they are named and wherever they are, will have social and economic consequences both foreseen and unforeseen.

One of those consequences is the possibility of a united Ireland – a prospect that terrifies me if the process of getting there is not given the time and breadth it needs, and if that existential, constitutional question it is not curated with the utmost inclusiveness and sensitivity.

Last week Varadkar stated the obvious when he told the MacGill summer school that a hard Brexit would force communities in Northern Ireland to consider the possibility of a united Ireland. They already are. What was once an entirely fringe aspiration for nationalists, and a dreaded fear for unionists – each side comforted by the thought that the conversation about unification was decades away – has become an urgent debate for all.

Expecting Ireland to be servile is part of a long British tradition | Richard McMahon Read more

Contrary to anti-Irish tropes that the backstop is a Trojan horse in order to secure a united Ireland, the truth is that both communities in Northern Ireland – as well as citizens across the island of Ireland – are fearful of what a botched, rushed conversation about unification might yield. That fear is that the birth of a united Ireland would be accompanied by violence and upheaval.

Unification without the support of unionists, whose traditions and identity must be protected as part of any shared future, cannot be pursued as a zero-sum game. Otherwise we risk repeating history: the Troubles in reverse. Northern Ireland could not, in its current perilous state, survive either a hard Brexit or a united Ireland. Its communities are suspended in an in-between space, in which they have enjoyed 21 years without violence but have not yet progressed to a positive peace or meaningful integration – a process that takes time and effort to heal wounds.

What many people in the UK forget or are indifferent to is the fact that, for all the successes of the Good Friday agreement – a vital edifice that allows us to identify as British, Irish or both – peace is not fully won.

That is why all the trash talk is so damaging, and why we need to pull back from the rhetorical brink. That is what is lost in this war of the Ultras: that the price of political power could be the unforgiveable loss of peace.

• Dearbhail McDonald is an Irish commentator and the author of Bust