Whether a “Remainer” or a “Leaver”, no-one welcomes chaos. So it is time for everyone to reflect and consider. Time to turn to reality – not fiction. Reason – not ideology. We need to calm the markets. We need to protect the economic wellbeing of the British people. We need to protect our national interest. There is absolutely no doubt in my mind that – to do so – we need to revoke Article 50 with immediate effect. The clock must be stopped. It is clear we need the most precious commodity of all: time.

Wherever one looks, a new world is forming: it is vigorous, and often contemptuous of old thinking. For a long time democracy, free trade, and the spread of liberal politics seemed unstoppable: we now know they were not. This illustrates a new dilemma for Britain – and for Europe. For decades, Britain’s overseas presence has been boosted by our close relationship with America, and our membership of the European Union.

But, America now appears to be moving away from us both – at the same time as we are moving away from Europe. Britain, shorn of these longstanding allies, is suddenly seen by the world as a mid-size, middle-ranking power, that is no longer super-charged by her alliances. This will surely diminish our international influence. Don’t misunderstand me: the UK will still matter – she is an amalgam of four proud and important nations – but she will matter less than once she did.

But the UK leaving the EU is a double loss: the EU is weakened, too.Europe loses its second largest economy, and one of only two European nuclear powers, with a significant military capacity. It loses a nation with a worldwide foreign policy reach.

This week is the 25th Anniversary of the signing of the Downing Street Declaration. The Declaration did not bring peace, but it did halt violence and bloodshed, and was an essential preliminary to the Good Friday Agreement.

Brexit has already inserted its very own poison into the turbulent politics of Northern Ireland. It begins with the DUP’s support for Brexit, which is flatly opposed both by their business base and by the majority of voters in Northern Ireland. It continues with the Confidence and Supply agreement the DUP reached to support the minority Conservative Government at Westminster. It may – on occasion – do so, but any formal support has the secondary (and inevitable) effect of undermining the UK Government’s role as an independent and honest broker in solving any problems between the two traditions in Northern Ireland.

The enthusiasts for leaving the European Union like to present it as a great and confident liberation. It is not. It is a retreat, not a liberation. A more confident United Kingdom would be remaining within Europe, reforming it; not complaining about Europe and leaving it.But that is not the view of the Brexiteers. Their apparent belief that Europe “gangs up” against the UK, and that the Commission “bullies” the UK, is not only absurd, it is embarrassing. On one day, they boast that a “global” United Kingdom can successfully “go it alone” in the world; the next day, they complain that the UK is being “bullied” by mere officials. There is a disconnect in logic here. They really must decide whether we are the United Kingdom or Little England.

Any border between North and South risks re-awakening memories of the worst of days; nearby graveyards bear witness to how bad were those days. No sensible person can wish to return to them. A border would not just be a trade barrier. It would be a visible manifestation of “us” and “them”. Under the Withdrawal Agreement, a new border is deferred while – for the time being – the UK remains in a Customs Union, until a technical solution is available to cope with trade formalities. But the problem is not over.

No-one should underplay the Anglo-Irish relationship. The UK exports more to Ireland than to China. Over 7,000 Northern Ireland companies trade across the border to the South. Since 2000, UK exports to Ireland have more than doubled: Irish exports to the UK have risen by 80 per cent. We are a huge market for each other. I could go on: our links far exceed politics and trade – important though they are. As a Briton, I say – Ireland is important to us and – in or out – of Europe that will not change.

Our duty – if we are to part company from the European Union – is to build on our relationship and not let it fragment. We British owe that to Ireland – and we owe it to ourselves. We can do this. We should do this. And we must do this.

This article is an edited version of John Major's speech to the Institute of International and European Affairs in Dublin today.