Ben Lowry: There is a growing risk of a no deal Brexit, which imperils Northern Ireland’s full status within the UK

The Second World War, perhaps, which could have led to internal disorder in NI that was a disastrous distraction from the war effort

That did not happen, despite some IRA activity. Even so, Winston Churchill at Britain’s most vulnerable point, 1940, offered Irish unity to Eamon de Valera in return for his support against the Nazis.

The 1950s IRA border campaign was also a potential peril to NI, but it was a flop.

The sudden momentum of the civil rights movement at the end of the 1960s, and the subsequent Troubles could easily have led to British exhaustion and disengagement, particularly after Stormont was prorogued in 1972. Abandonment was considered then by the Tory prime minister Edward Heath.

The Anglo Irish Agreement of 1985 was the biggest single blow to unionism after 1921, and an accord from which we will never fully recover, even though the 1998 Belfast Agreement was a partial recovery.

Yesterday this paper ran a fascinating letter (see link below) from a reader who expressed dismay at the failure of unionists to defend the Good Friday deal against nationalist attempts to use it to justify their own advances.

That failure is rooted in unionist ambivalence about the Belfast Agreement, ambivalence that is increasingly widely felt as a terrorist narrative is fast rehabilitated – albeit obliquely, by denigrating the state in conspiracy theories (implying that paramilitary and security forces were about the same).

Far from lessening with time, the divisions over the legacy of the past are worsening. If anyone thinks that appeals to republican politicians not to celebrate the IRA are going to have any effect, forget it — such a view of history will become more mainstream as the exaggerations about past British brutality gain ground.

The latest huge challenge to Northern Ireland is Brexit, yet it hasn’t even happened.

The period after the 2016 referendum was a ‘phoney war’. Some of us feared that Brexit would have disastrous consequences for the Union with Scotland or here, and perhaps both, yet things were surprisingly mute until well into 2017.

In the last year however the bitterness has grown. Irish nationalism, on both sides of the border, is increasingly emboldened against Brexit, supported by the political centre ground in Northern Ireland.

In a diplomatically worded, but ultimately blunt, article on these pages yesterday (see link below), the anti Brexit academic Professor Colin Harvey said that the conversation about how we share this island “has changed”.

The EU chief Brexit negotiator Michael Barnier will hardly be inclined to compromise on the backstop after he saw the NI MEP contingent change from two unionist/one republican to one DUP/two anti Brexit (Naomi Long was filmed by the BBC alongside a Sinn Fein MEP telling Mr Barnier she hoped his “patience had not expired”).

Now people as influential as Michael Portillo are suggesting a return to the Northern Ireland-only backstop, that guarantees a border in the Irish Sea.

There was also the recent poll that suggests more Tories want to see Britain leave the EU than see the UK itself survive. The pro Brexit commentator Julia Hartley Brewer appeared to endorse such thinking.

This is one reason why it was important that the DUP denied it was prepared to support the backstop in return for funding for Northern Ireland, when it emerged that the chancellor Philip Hammond had met the party prior to the March vote on the Withdrawal Agreement.

The last thing we need in this climate is English nationalists thinking that Northern Ireland’s principal loyalty is to money.

On Monday I was at a talk at Dublin’s IIEA (Institute of International and Economic Affairs) by Douglas Carswell, the Tory MP who defected to Ukip (before falling out with Nigel Farage, then losing his seat).

Mr Carswell, who spoke well, said that such opinion polls, in which voters are given a binary choice between two unpalatable options, are not reliable gauge of what they would do on reflection.

Even so, I think we are in the grip of a near mania on Brexit.

An issue that had marginal support 10 years ago must now, in the wishes of a large section of the British population, be delivered to the fullest possible extent, regardless of the repercussions for the very unity of a nation that not so long ago fought to retain a tiny piece of distant territory, the Falklands, in the South Atlantic.

There is a plausible case for a no deal Brexit, but only if there was much higher backing for leaving the EU, 60% plus, and a greater geographic spread in that support (all four home nations and London).

Mr Carswell articulated a persuasive case that Theresa May had made a grave mistake in accepting that the UK had to ask permission to leave the EU, and that the Irish border had to be tied down in perpetuity before we even left.

He pointed out that the EU had been intransigent on the only thing, the backstop, that had prevented the deal being passed by MPs.

But he seemed to be on shaky ground when a member of the IIEA audience put it to him that UK support for Brexit had not been particularly strong in the MEP elections.

Mr Carswell said that some people were adding up the votes in a way that allowed them to think there was a majority against Brexit. But the evidence is stronger than he says. While 34%of voters backed the Brexit Party or Ukip, many of the 23% who voted Tory and Labour oppose Brexit. The other big parties and their supporters are passionately so. At most a narrow majority of UK voters were pro Brexit in that election, and perhaps not even that.

I suspect Brexit would win a second referendum, but support for it has not leapt upwards since 2016. The mandate for no deal is weak, yet it is closer than we might think.

I have long thought a general election is hard to avoid but it is almost certain if no deal nears. Mr Carswell thinks no deal now likely, even if Jeremy Corbyn has most MPs after such an election.

Other respected voices think so too. Ivan Rogers, ex UK representative to EU, thinks no deal is more likely than not. Dan O’Brien, economist at IIEA, thinks similarly. When I was in BBC NI recently, I asked its business editor John Campbell the likelihood, and he put it at 50%.

London has already shown that one of its top priorities in event of no deal will be placating Dublin.

The prospect of Jeremy Hunt being robust towards the Irish seems slim, and Boris Johnson, who voted for the disastrous backstop despite his tough talk against it, might just push through a Brexit that means a permanent Irish Sea border.

• Ben Lowry (@BenLowry2) is News Letter deputy editor

• Colin Harvey: Some unionists are likely to suffer as a result of Brexit, but is little conversation about that

• Letters: Unionists are allowing nationalists to make advances behind the 1998 Belfast agreement