Theresa May has confirmed that the Conservatives will rely on their “friends and allies” in Northern Ireland’s Democratic Unionist Party for a majority in the next parliament.

That concession rounds off a spectacular night for Arlene Foster’s party, who increased their tally of seats from eight to 10 – and will now be the only Northern Irish party sitting in the Commons (Sinn Fein, who do not take their seats, won seven of the remaining eight, with independent unionist Lady Sylvia Hermon making up the numbers).

So what might this mean in practice? The DUP were among the most enthusiastic advocates for Brexit, but that is not to say they share the priorities of the hard leave wing of the parliamentary Tory party.

Its leader Arlene Foster – who since leading her party to a historically poor result in March has undergone a remarkable transformation from liability to asset – has said as much, and very explicitly indeed. “No-one wants to see a ‘hard’ Brexit,” she said last night. “...We need to do it in a way that respects the specific circumstances of Northern Ireland, and, of course, our shared history and geography with the Republic of Ireland.”

And so the DUP will not countenance a dilution of Northern Ireland’s integral place inside the UK, such as the special EU status proposed by nationalists. But it also will not and cannot accept a Brexit that imposes a hard border or excessive economic disruption on the island of Ireland.

Unionists in the North are wont to dismiss calls from Irish politicians like Leo Varadkar, who will succeed Enda Kenny as Taoiseach later this week, for Northern Ireland to remain in the EU single market as a special case. But in practice they want the same thing - for their island to remain, for the most part, completely economically integrated.

In this respect, the left’s broad-brush characterisation of the DUP as the Tories’ Ukip wing on steroids is much too blinkered to reflect the complexity of the relationship to come. On the Irish question – one of the European Commission’s top three negotiating priorities – May is now outflanked both by Brussels and her parliamentary allies.

Paradoxically, her reliance on this one set of Brexiteers – who will do all they can to seek the softest of exits – will embolden the subversive instincts of the Eurosceptic old guard within her own party. So on the very issue with which May defines her premiership, the presence of the DUP will exacerbate rather than soothe her parliamentary headache over Brexit.

The party’s economics are much wetter than media caricatures would suggest. The likely need for financial inducement will drive a bulldozer through Tory manifesto commitments such as abolishing the triple lock on pensions, the bedroom tax, and hasten the abandonment of austerity. They may well demand the replacement of EU grants in full by central government. Little wonder that NS contributor John Bew once likened the Northern Irish parties’ attitude to public subsidy to “the SNP on crack”. It is unlikely to reassure those who derided the supposed redness of May’s Toryism during the election campaign. Though the parliamentary arithmetic is reassuring, any stability will prove very illusory indeed.

So too in Northern Ireland, where many - especially women and minorities - could pay a high personal price for the Conservatives’ reliance on the DUP. If there was a slim possibility that HM Government would intervene and extend the provisions of the 1967 Abortion Act to Northern Ireland, it has now gone. Governments have been here before. Though much has been made of the ideological synergy between the Tory right and DUP, this was a price Gordon Brown’s government was willing to pay in order to secure the passage of anti-terror legislation in 2008. It has been almost two years since Belfast’s High Court ruled that Ulster’s restrictive abortion laws breached human rights. Now more will pass before there is any substantive reform.

The same can be said of equal marriage, which the DUP repeatedly blocked at Stormont using the assembly’s petition of concern mechanism. The party’s attitude towards the issue was expressly criticised by Martin McGuinness, the late deputy first minister, when he resigned in February. There had been a quiet consensus at Stormont that the Northern Ireland Office would do much of the heavy lifting on the culture clash issues that divided the two parties, such as equal marriage, and legislation on the Irish language, so as to ensure neither appeared culpable to their respective bases.

Now Sinn Fein has all the incentive it needs to play to its own. A Republican source told me last night result meant Northern Irish politics had been “changed utterly”. They are right. The restoration of an executive – which the DUP leadership is keen to facilitate – is now even more implausible, and in nationalist eyes HM Government’s ability to act as an honest broker in negotiations has completed evaporated.

But given the fragility of May’s majority – and the febrile atmosphere within the Tory ranks – the price of DUP cooperation may well be the collapse of government at Westminster, as well as at Stormont.