We’ve seen a rash of headlines on the likely fate of Brits who live in EU countries – and EU immigrants in Britain – following a Leave vote on 23 June.

The Telegraph ran a story this week saying: “Three million EU citizens in the UK could be deported if Britons vote for a ‘Brexit’, Home Office suggests.”

Several papers have also reported that British expats in Spain are worried about their future too.

The fear is that Britain would no longer have to guarantee the “free movement” rights of EU citizens to live and work in this country, and Brits who have settled in Europe would lose the same rights.

But Leave campaigners have said the fears are unfounded, saying the Vienna Convention on the Law of Treaties will protect everyone’s free movement rights.

International law can be tricky for the layman to interpret, so we asked a number of leading academics who specialise in these areas for their views.

Unusually, there was almost complete agreement from our expert panel. This is what they said…

EU citizenship ends with Brexit

If Britain withdraws, Brits will no longer be EU citizens, and EU citizens will lose their right to live in the UK based on the EU treaties.

Any arrangements that allow UK citizens to continue to live and work in the rest of the EU – and the other way around – will have to be negotiated.

Some treaties specify that “acquired rights” which people enjoy while the agreements are in operation should continue after they are terminated.

But Article 50 of the Treaty on European Union – which allows member states to leave – makes no mention of acquired rights.

The Vienna Convention won’t help

The chief executive of Vote Leave has said that the 1969 Vienna Convention on the Law of Treaties ensures that the free movement rights people enjoy under EU law will continue after Britain leaves the bloc. This was contradicted by every expert we spoke to.

Professor Jo Shaw from Edinburgh University said: “The references to international law protecting individual rights are profoundly misleading.”

This is because the Vienna Convention protects the rights of states, not individuals, as several legal commentators have made clear over the years.

Things protected by the convention would probably be limited to areas like a contract of employment or the ownership of property abroad, rather than the blanket right to live or work in another country, said Professor Damian Chalmers from the LSE.

He said the Brexiteers’ argument created an “absurd situation”: if everyone had the same rights after Brexit that they had before, Britain would not be able to change any EU laws.

“Then there would be no point in leaving the EU,” he added. “It’s a very opportunistic argument that they are using.”

Jean-Claude Piris, former head of legal service of the EU’s Council of Ministers, has also talked of the “absurd consequences” of this theory: “Acquired rights would remain valid for millions of individuals (what about their children and their grandchildren?) who, despite having lost their EU citizenship, would nevertheless keep its advantages for ever.”

Neither will EU law

Vote Leave say: “EU law forbids the collective expulsion of British citizens living in the EU.” They provide a link to the EU’s Charter of Fundamental Rights, which does indeed say: “Collective expulsions are prohibited.”

Again, the experts were not impressed, with several pointing out that the charter only applies to member states when they are applying EU law. If Britain was no longer in the EU, it’s not clear that this would apply to British citizens.

In any event, Professor Chalmers told us: “Prohibitions on collective expulsions… merely require that each case be heard individually, and not that people of the same nationality cannot be expelled.

“UK citizens could be expelled. Procedures would just have to be followed in each individual case.”

But no one is talking about mass deportations anyway

The Telegraph headline claimed ministers are suggesting that 3 million EU citizens “could be deported” from the UK, but that’s not really what the government said.

Lord Keen of Elie, the Home Office spokesman for the Lords, said in a statement: “UK citizens get the right to live and work in the other 27 member states from our membership of the EU.

“If the UK voted to leave the EU, the Government would do all it could to secure a positive outcome for the country, but there would be no requirement under EU law for these rights to be maintained.”

There is no mention of anyone being deported here. What we are talking about is a change of legal status, which would have different implications for different people.

Professor Shaw told us: “I don’t think anyone says you are going to have a collective expulsion of the type we saw, for example, in East Africa. Or some sort of ethnic cleansing as we saw in the Western Balkans/former Yugoslavia in the 1990s.

“The correct legal position would be to say that case-by-case people may find that what they assumed was a secure legal status is no longer such a status.

“That will be at the very least worrying, and it will also be the case that some might find themselves, because they lack a legal status under post-Brexit national immigration law, subject to individual enforcement action, just as those who overstay their visas, for example, in the UK are subject to enforcement action.”

Dr Helena Wray from Middlesex University said: “It would be difficult under national and human rights law to remove long-standing residents who entered on the basis that they could remain and who have made a life for themselves here. Those who have not been here for a lengthy period would be more vulnerable.”

Professor Sionaigh Douglas-Scott from Queen Mary University of London said: “A far as I can see it, it’s not so much a matter of collectively expelling anyone as, post-Brexit, not giving them the privileges EU citizens get.

“Instead, after a Brexit, without further negotiated protection, British citizens would be in the same position as other third country nationals living abroad.”

There will have to be a compromise

Again, everyone we spoke to agrees on this. Practically speaking, the British government will not want to be seen to be dealing harshly or unfairly with EU migrants who have made this country their home.

If it did, it would risk reprisals from countries like Spain with large British expat populations.

Professor Eleanor Spaventa from Durham University said negotiations could be complicated, with workers, students and pensioners potentially getting different deals.

She said the most likely outcome would be that EU workers currently employed in the UK who suddenly lose the right to work would be issued work permits, while EU citizens who have permanent residence after living here for five years may get to keep that right to reside.

We might keep freedom of movement anyway

Many believe the most likely post-Brexit scenario is that Britain would leave the EU but stay in the European Economic Area, like Norway, Iceland and Liechtenstein.

EEA countries have to uphold the same “four freedoms” as the EU countries – the free movement of persons, goods, capital and services.

In this scenario, EU citizens will carry on enjoying the same rights as they do now. Of course it remains to be seen whether UK voters would accept such a compromise if reducing immigration from the EU was the main reason they voted to Leave.

The verdict

The consensus from our experts is that the Leavers are wrong on the law – but right to tell people not to worry too much about the prospect of being deported, either from or back to the UK.

That probably won’t happen, but not because of the Vienna Convention on the Law of Treaties, which all our academics thought was a red herring.

It won’t happen because it won’t be in anyone’s interests, so some kind of political compromise will have to be found.