A triumph. A turning point. A bold new beginning. It is a measure of how far Britain has fallen that, nearly seven years after the Brexit vote, a decision to stop fighting with the European Union is hailed by ministers as a diplomatic feat for Rishi Sunak.

After the lies of Boris Johnson and the chaos of Liz Truss, it seems churlish to begrudge the prime minister a plaudit or two for seeking an intelligent resolution of the dispute about the Northern Ireland protocol. The deal should yield measurable dividends - not least the avoidance of a slide towards a trade war with Britain’s most important economic partner. No-one should imagine though that it changes the essential facts of Brexit.

With the lack of self-awareness that is the trademark of Conservative Brexiters, Sunak admits as much. The new trading arrangements for Northern Ireland, he declares, promise to turn it into one of the world’s most “exciting” destinations for foreign investment. It confers on the province the unique advantage of frictionless trade with both the single market and with the rest of the UK. “No-one else has that”. All parts of the UK, of course, shared the benefit until Brexit.

The terms struck with European Commission president Ursula Von de Leyen were unsurprising - a judicious mix of practical adjustments and, in matters of political theology, of constructive ambiguity. They could have been agreed a year or more ago had Johnson’s mendacity not drained of all trust the government’s relationship with the European Union. Sunak’s strongest card was his perceived integrity. The assurance that the Brits would not renege a second time supplied the space for the Commission to make sensible compromises.

The prime minister has still to navigate the domestic politics. The Democratic Unionist Party is against any arrangement that marks out Northern Ireland as different from the rest of the UK. For the hard core of Brexit ultras on the Tory back benches conflict with Brussels is an ideological imperative. Johnson, the author of the mess, has still to come to terms with the abject failure of his premiership. He has set as his mission toppling Sunak.

The sense of Westminster, however, is that the momentum is with the prime minister. A nation in deep economic crisis has tired of the Tories forever blaming the Europeans for the nation’s manifest woes. The Democratic Unionists face an uncomfortable choice. If they continue to boycott the Stormont assembly, Northern Ireland will be governed by London in collaboration with Dublin. Unionism will lose its voice. Sunak has travelled too far to surrender to his party’s ultras. To do so would leave him killing time for the rest of his premiership.

A settlement will see doors open again after Britain’s unsplendid isolation during the Johnson/Truss era. A summit in Paris with Emmanuel Macron next week, the first such high-level meeting for five years, may actually yield results - plans for sensible cooperation in areas like defence, energy security, and, politically vital for Sunak, curbing the channel crossings of undocumented migrants.

The White House has yet to confirm Joe Biden will travel to Belfast next month to mark the 25th anniversary of Northern Ireland’s Good Friday agreement. There is diplomatic talk of a state visit to coincide with the trip. Whatever the precise choreography, Sunak can now expect a thaw in a special relationship that had become more than frosty. Brexit diminished the UK in American eyes. That will not change. The shock, though, was see the Northern Ireland dispute reduce Downing Street’s voice in the White House to one of irrelevance.

The thaw will extend to Brussels. The hope must be this is a first step in a process of normalisation. Von der Leyen has already indicated that talks can resume on British participation in the Euros 95 billion Horizon scientific research project. There are half-a-dozen other irritants in the relationship that can now be addressed, including perhaps, the visa regime for temporary workers. Britain cannot expect to be showered with benefits but, in the characterisation of one French diplomat, the answer will no longer be an automatic “Non”.

For British as well as Northern Ireland business, the dividend will come in terms of greater certainty about the economic relationship with customers, suppliers and partners across the European Union. The background threat of a trade war has been a constant brake on trade and investment. There is now at least a possibility that the scheduled 2025 review of the trade and co-operation agreement will see an easing of barriers.

No-one should think that any of this changes the fundamental impact of Brexit. Britain will not recoup the national income lost to its departure from the Union. Businesses will continue to trade at a disadvantage to their French and German peers. The government will not recover the opportunity to shape events that came with its presence in Brussels.

Brexit was seen by its advocates as an event. It’s a process. Britain cannot escape its geography. Its prosperity and security are rooted in Europe. It has struck out on its own at a moment of geopolitical upheaval that has driven other European democracies closer together. A grown up relationship with Brussels can mitigate the damage. No more than that.