The history of Northern Ireland since 1920 demonstrates the danger of attempting to impose, by a simple majority, a constitutional settlement, and an identity, on a minority who feel they have been overruled.

Those pressing for an early border poll on Irish unity in both parts of Ireland should reflect on this. Such a poll could repeat the error of 1920 and add to divisions, rather than diminish them.

I was a bit surprised, then, to see Bertie Ahern call for a border poll in 2028 (the 30th anniversary of the Good Friday Agreement). He knows how fraught things could become.

Setting target dates, without having first done all the groundwork and collected all the data, can lead to unintended consequences. Target dates tend to be misinterpreted as promises.

We should also learn from the experience of the 2016 UK Referendum on Brexit.

Reducing a complex issue, with many nuances and gradations, to an over simplified yes/no question is hazardous in itself. Setting target dates for a referendum before any details have been worked out, is even more so. As 2016 has shown, it can also lead to the oppression of minority viewpoints, lasting division and to unforeseen consequences. For these reasons, I was also surprised to see Sinn Féin spending large sums in advertisements in the US, calling for early referenda on Irish unity, without reference to what it has learned from the Brexit referendum.

The Good Friday Agreement (GFA) does indeed provide for such a poll to be called, on the basis of a political judgment by the UK government. Oddly, it does not require them to consult with the Irish Government, even though a poll would also have to take place here too.

Even though all other legislative decisions in Northern Ireland must, under the GFA, be agreed by a procedure of parallel consent of both nationalists and unionists, this, seminal and possibly irrevocable, decision can be taken for Northern Ireland, by a simple majority of just one vote in a referendum.

As Seamus Mallon recognised, this is a recipe for trouble. It sits uncomfortably beside some of the principles in the Downing Street Declaration of 1993, agreed by Albert Reynolds and John Major.

Two governments

That declaration is the foundation on which the GFA, and the entire peace process, was built by the two governments.

The wise words of the Downing Street Declaration should influence both:

The Downing Street Declaration says that Irish unity should be achieved “by those who favour it, persuading those who do not, peacefully and without coercion or violence”.

I do not think a poll in favour of unity carried by a small margin, and before a majority of the unionist community have been persuaded of the merits of Irish unity, could truly be said to meet that criterion.

It might be legally valid, but not politically wise.

There is little evidence that this type of persuasion is taking place within Northern Ireland between the two communities. In some senses, they are more polarised than ever and are talking past one another.

The Sinn Féin advertisements advancing arguments for unity should have been in the Belfast Telegraph or the Newsletter rather than the New York Times.

I do not see much evidence that those who say they want an early border poll are putting forward concrete ideas to persuade unionists to cease to be British unionist, and instead embrace Irish unity. What have nationalists said to them so far, that would show them how their British heritage and ethos would be respected in a united Ireland?

In the same declaration in 1993, the Taoiseach Albert Reynolds said on behalf of the Irish people: “Stability will not be found under any system which is refused allegiance, or rejected on grounds of identity, by a significant minority of those governed by it.”

This was a humane and realistic statement.

I do not think a poll on unity, carried by a narrow majority of say 51% to 49%, could be guaranteed to deliver a system that would not be “at risk of being rejected, on grounds of identity, by a significant minority”. If it were, there would not be much stability.

It is also important to recognise that the GFA itself says that, regardless of the constitutional status of Northern Ireland, there must be “full respect for, and just and equal treatment for, the identity, ethos and aspirations of both communities”.

Those who favour a border poll have an obligation to spell out exactly how the British identity, and monarchist ethos, of the unionist population might be given the required “equal treatment and respect”, across the whole island in the wake of Irish unity.

This will not be easy. Some of the changes required might go against public opinion here.

The recent furore about commemorating the dead of the RIC, 100 years after they were killed, is a foretaste of the sort of resistance that might be encountered. Symbols can be very divisive.

Domestic taxation

There could also be implications for levels of domestic taxation here, as the UK subsidy to public services in Northern Ireland at present, comes to 20% of GDP there.

It is also important to stress that a border poll in favour of unity in both jurisdictions might not necessarily settle the constitutional issue finally, especially if the margin was narrow.

Paragraph (v) of the GFA will oblige the government of a united Ireland to continue to respect the “aspirations” of the unionist community, in what was Northern Ireland. It is quite likely that, in certain areas, large local majorities would continue to aspire to rejoin the UK. North Armagh, east Belfast, Antrim and many other places come to mind.

Even if such a continuing existence of such an aspiration did not pose a security risk, it is an aspiration that the authorities would, in any event, be obliged to respect under paragraph (v) Good Friday Agreement.

On the face of it, this is not a recipe for stability.

I believe the focus now should instead be on making all the three strands of the Good Friday Agreement yield their full potential, rather than fixating on territorial sovereignty through a border poll.

Personally, I would like to see Irish unity, but we must first build sustained reconciliation, and shared goals, between the two communities in Northern Ireland. That is a commonsense precondition for success.

The voters of the Republic of Ireland, who would also have to vote in a poll on Irish unity, would need to ask themselves, before they vote, if the criteria for Irish unity, set out on their behalf by Albert Reynolds in the Downing Street Declaration, 1993, have been met, or are likely to be met as a result of the poll.

That will be a heavy responsibility.

Let us think this thing through, and avoid precipitate commitments to dates for referendums, before every angle has been figured out.