EU exit: two million could become illegal immigrants overnights says former attorney general

In an attack on Eurosceptics in the Conservative party Mr Grieve was critical of those who want to withdraw from the EU and the European Convention on Human Rights (ECHR).

Mr Grieve’s comments come ahead of the publication of the party’s election manifesto next month which is likely to commit the party to withdrawing from Strasbourg’s jurisdiction.

Some sources suggest the desire to withdraw from the ECHR is cooling at Downing Street, with Russia and other matters threatening European unity.

However, the party has unequivocally promised a referendum on EU membership.

In a lecture in London entitled “Britain’s International Obligations – Fetters or Keys?” Mr Grieve warned that leaving the EU would create more problems than it would solve.

The former attorney general said: “The requirements of any free trade agreement would make British removal from the clauses dealing with freedom of movement impossible.

He said this would leave the biggest cause of domestic irritation with the EU – immigration – unaltered and added: “But without its maintenance some 2 million UK citizens working in EU countries would find themselves becoming illegal immigrants overnight.”

Mr Grieve, who was sacked during the last cabinet reshuffle after he opposed Conservative calls for the UK to withdraw from the ECHR, is now also warning about adopting a policy of “isolationism”.

He said: “There is … a total lack of clarity as to how a government would proceed to unravel a relationship that has developed in complexity over more than 40 years.

“Which parts of the several thousand pieces of EU legislation that are currently incorporated into our own statute law would be retained?”

On the ECHR, Mr Grieve added: “The success of the convention, despite all its shortcomings, in raising standards of behaviour and promoting human rights globally, and with it the overall security of the Europe, is to be disregarded for the sake of addressing irritations about some of its current domestic impacts which at best will be of utterly marginal benefit.”

In relation to “rejectionism” and isolationism, he said this new mood was at odds with the UK’s tradition of nurturing relationships and respecting obligations.

He said: “We are an outward-facing nation with a global language, a global cultural, educational and legal reach,” with, he added: “deep ties all over the world and with one in 10 of our citizens living permanently overseas…

“We should build on what is on offer and not hanker after some simpler world that does not and has never existed.”