Given the centrality of the notion of free movement to the idea of the EU it is perhaps surprising that it was only in the Amsterdam Treaty, agreed last summer, that such issues as immigration control and asylum policy were brought fully into the arena of EU collective decision-making. Yet these are questions which touch deeply on our notions of national sovereignty.
Under Maastricht they remained matters for co-operation between member-states unlike the movement of goods, the rules for which are a Community competence. New provisions in the Amsterdam Treaty, which will only come into force once ratified by all the member-states, allow five years more of unanimity voting, after which majority voting will apply to such issues.
The new treaty also brings under the wing of the Union the quite separate Schengen Treaty on internal passport-free travel, whose provisions in many respects duplicate those of the EU. It was signed by 13 EU member-states as well as Norway and Iceland.
Ireland and Britain, the nonmembers, have been given the oppportunity to opt into those aspects of the treaty provisions which appeal to them, such as enhanced intelligence collaboration. Their insistence that it is easier for them, as islands, to control immigration at point of entry is now widely understood and less seen as an anti-European gesture, and the Amsterdam treaty explicitly recognises the common travel area between the two countries.
Schengen provides elaborate rules and procedures - running to some 1,200 pages - to cover such issues as common visa and asylum rules, the measures taken by member-states at the Union's external borders, and the monitoring of the flow of immigrants within the Union. Most importantly there is also a duty on member-states to participate in the computerised database established by the treaty, the Schengen Information System.
(The latter, already seen as Big Brother in Denmark, and a potent argument for "No" campaigners in the referendum, was recently the source of considerable embarrassment to the authorities when two Belgian policemen were found to have been selling information from the computer to criminals.)
Only when a member-state can assure the rest that it can effectively seal the Union's external borders will they then agree to lift passport controls with it internally. This has led to Italy and Greece, although members, being kept out in the cold until now.
In December a Schengen decision was taken to accept Italian controls and to lift frontier checks to the rest of the EU from March, although not yet in Greece. But the influx since then of Kurds, most of them using Italy as a transit point, has led to blazing rows between Italy and four of its partners, Germany, France, Austria, and the Netherlands.
The Germans, already in election mode, have been particularly vociferous, with calls to seal the Italian border and repudiate Schengen. These have been fuelled by the willingness of the Italians to allow suspected illegal immigrants to remain in the country in special open refugee camps for 15 days to prove on appeal that they are genuine asylum-seekers and under threat if returned home. If they can do so, Italy has an obligation to keep them.
It is a basic rule of international asylum law, arising from the 1951 Geneva Convention, that there is a prohibition on the direct return of refugees claiming asylum to the country they came from - known as refoulement - if they can establish that they face persecution. Nor may they be sent to a country which is unlikely to honour that obligation, a fear expressed by Human Rights Watch over the return to Turkey of asylum-seekers who can be shown to have come through Turkey.
The EU has practised the principle of the "safe third country" to return asylum-seekers for assessment to "safe" countries through which they have travelled to get to the EU.
But the system for determining which countries are safe has been attacked by the UN High Commissioner for Refugees and is a particular problem with regard to Iraqi Kurds in Turkey who may face persecution either from the government or from one of their own warring factions.
And states are also required to ensure that the decision to refuse asylum is not taken by a junior border guard or official but by due judicial process and individually - hence the Italian delays. The Italian willingness to insist on due process has been praised by Human Rights Watch.
Meanwhile, it is now almost certain that the Schengen executive committee will reverse its decision to approve the Italian control system and that checks will remain in place on the Italian border.
The row has led to suggestions, particularly in the British press, that Schengen is fatally flawed and on the point of collapse. Not so, say officials. The crisis, they believe, has shown the need for more co-operation, not less, for more Schengen, not less.
According to the officials, the reality is that the length of the common internal borders and the huge volume of trade across them make inevitable a move away from a passport-based border system of controls to one based on pooled intelligence. "The only really secure border in Europe," one official says, "was the Berlin Wall." Them days are gone.
