Garvan Walshe is a former National and International Security Policy Adviser to the Conservative Party. He runs Brexit Analytics.

Peace agreements are messy compromises, and the 1998 Belfast Agreement is just that. Terrorists of the IRA and UVF would make their way into politics. Sinn Fein and the DUP, the parties opposed to the compromise, would become its greatest beneficiaries. The distinctive selling point of the SDLP and Ulster Unionists — moderation and support for constitutional democracy — would evaporate. If a vote for Sinn Fein stopped being a vote for terror; and one for the DUP was no longer for Protestant supremacism, why not give full expression to your identity? As the Dr Pepper ad goes, what’s the worst that could happen?

The leniency with which terrorists were treated by the agreement; the ambiguities surrounding the decommissioning of their weapons; the sanitising by Mo Mowlem, the Northern Ireland Secretary, of paramilitary thugs beating young men to a pulp as “internal policing”; the failure of terrorist groups to account for their crimes, or to even provide families with the location of where the people they had “disappeared” for resisting them had been buried; all contributed to my decision to join the Conservative Party. Labour, pre-9/11, couldn’t be trusted to stand firm enough against terrorism.

9/11 changed that, but also the perception of “the troubles”. It caused their brutality in Northern Ireland — men forced, their families kidnapped, to drive trucks full of explosives into military bases as involuntary suicide bombers; families gunned down at home; the conversion of a few pints at your local into a dance with death — to disappear from memory. More importantly, they caused the United States, which had previously overlooked US funding of the IRA, to turn up the pressure. That fixed the biggest flaw in the Agreement, and forced Sinn Fein to become a more or less constitutional political party.

The Agreement recognises that territories divided along sectarian lines can’t be governed by majoritarian politics. It allows people to choose to be Irish or British or both. Margaret Thatcher was wrong to say that Belfast was as British as Finchley. But nor is it as Irish as Castlenock on Dublin’s south side, where Leo Varadkar cut his political teeth as a councillor. That’s why, beginning with Thatcher’s 1985 Anglo-Irish Agreement, through the 1993 Downing Street Declaration, in which John Major made it clear that the British government had no “selfish strategic interest” in Northern Ireland and that its constitutional status was a matter for its people to decide, it was understood that the six counties’ status was sui generis.

But this week’s co-ordinated attack on the Agreement by pro-Brexit figures is as irresponsible as it is unnecessary.

Irresponsible because Anglo-Irish relations are at the worst they have been for years despite having the most pro-British Taoiseach in office since John Bruton (cruelly if not entirely inaccurately nicknamed “John Unionist”); because even if Brexit did not impinge on Anglo-Irish relations, a government consumed with the negotiations in Brussels hasn’t the capacity for a second diplomatic effort; and, most of all, because a government dependent on the DUP for support would be unable to negotiate in good faith: the promise in the 1993 Declaration, that it has no “selfish strategic interest” in the status of Northern Ireland, would be broken and the entire basis of the peace process annulled.

And unnecessary because a meaningful Brexit for Britain can be achieved without risking peace in Northern Ireland. Though I personally favour a Norway-style compromise where Britain leaves the EU and stays in the Single Market and Customs Union, I understand why many Brexiters think that would defeat its purpose. Brexit has two main aims: for Britain to be able to set immigration policy, and make its own decisions on regulation and trade.

The problem of course is how to do that without imposing a hard border between Northern Ireland and the Republic. Without “creative solutions” that exist only as motes in the eye of ambitious public sector IT engineers, an independent trade and immigration policy are only possible if Britain leaves the Single Market and Customs Union. That is, and this is a matter of logic that cannot be fudged: if there’s to be no border on Ireland, and Britain is to leave the Single Market and Customs Union, it follows that there must be one on the Irish Sea, between those parts of the UK outside the Single Market and Customs Union, and Northern Ireland, which will stay in.

Though the DUP say they oppose this, it is in fact supported by Leave voters in Northern Ireland (64 per cent), Protestants (64 per cent), and supporters of unionist parties (59 per cent), according to research by John Garry for the King’s College ‘UK in a Changing EU’ centre. In reality, the DUP is divided between a hard-line faction based at Westminster and a younger, more pragmatic generation of leaders in Northern Ireland itself, who want to serve their Northern Irish constituents.

By trying to reopen the Belfast Agreement, Brexiters such as Owen Paterson, a former Northern Ireland Secretary, Dan Hannan and Kate Hoey showed that Brexit is so important to them they are willing to risk a return to violence in Northern Ireland to get it. But they can have Brexit for Britain without running that risk. In the agreement to move to Phase Two of Brexit talks, the government allowed the Northern Irish institutions to permit Britain to escape the Single Market and Customs Union membership that is now required to prevent a border in Ireland.

Brexiters’ efforts should now focus on persuading the DUP to allow Britain the freedom to diverge. It makes sense for the DUP: they avoid the hard border they say they oppose, and achieve an outcome that reflects the views of the communities they represent. It makes sense for the Brexiters, too. As the Prime Minister said in Munich, they shouldn’t let deep-seated ideology jeopardise the security of our citizens.