David Cameron says the decision on remaining in the European Union is the biggest the British people will make in their lifetime. What he does not say is that a decision to leave would constitute the greatest U-turn in modern UK politics.
Harold Macmillan concluded in 1961 that the UK's future lay not in a free trade area, but in a Common Market aspiring to an ever-closer union. That has been the keystone of British foreign policy ever since.
But some of the reforms now demanded by the Government constitute a repudiation of commitments repeatedly entered into by the UK.
• In the 1972 Treaty of Accession, the United Kingdom declared its "determination to construct an ever-closer union among the peoples of Europe".
• In the 1975 referendum, the people of the UK endorsed that commitment by voting "to remain within the Community".
• In 1985 Margaret Thatcher's Government signed the European Single Act promising "to contribute together to making concrete progress towards European unity".
• At Maastricht in 1992 John Major's Government pledged "to continue the process of creating an ever closer union among the peoples of Europe".
Now Mr Cameron says he wants no part of "an ever-closer union" and demands it dropped.
He also demands that there will be no single currency for the EU; that though the euro is the currency of most member states, it will not be the currency of Union.
Yet, in 2007, the United Kingdom agreed in the Lisbon Treaty that "the EU shall establish an economic and monetary union whose currency is the euro". The UK's opt-out does not negate that.
The "ever-closer union" first appeared in the Treaty of Rome as the founding aspiration of the pioneers of integration after the Second World War. It remains an aspiration, reaffirmed in treaty after treaty. It is not a binding commitment to any specified goal, but to remove it would be an act of great symbolic importance. It would be tantamount to saying that the European project is over; integration has gone far enough.
Mr Cameron may think so, along with most of his party and a significant proportion of the British public, but can he convince 28 other member states to accept such a brutal abandonment of a cherished if undefined aspiration? Or is this particular demand a bargaining counter that may be quietly dropped or fudged when the bargaining begins?
It is ironic that the United Kingdom should be leading the drive against integration when the whole purpose of integration was and is to prevent the continued repetition of the catastrophes brought about by nation states' inability to resist the virus of extreme and violent nationalism.
The Second World War was the darkest chapter in that tragic history, which very nearly saw the annihilation of the United Kingdom. The UK has been the major European country most threatened by disintegration resulting from nationalist demands and which has suffered most from terrorism driven by extreme nationalism.
The EU today faces massive problems - Russian aggression, the refugee crisis, turmoil in the Middle East, climate change, sluggish economic growth. All of these demand co-ordinated European responses, which can come only from a stronger, more integrated, European Union.
Nearer to home, a decision to leave the EU would almost certainly ensure a Scottish breakaway, probably finish off the ailing Northern Ireland "peace process" and hasten the disintegration of the United Kingdom.
Dennis Kennedy is a former deputy editor of the Irish Times and served for a term as European Commission representative in Northern Ireland