There is a "Senior European Experts Group" which is an independent body consisting of former high-ranking British diplomats and civil servants, including several former UK ambassadors to the EU, and former officials of the institutions of the EU. It has published the following briefing note on rights of migrants.
"Around 13.6 million EU nationals live in another Member State of whom 6.5 million are known to be in employment (the latter does not include those who are self-employed). In addition, a substantial number of EU nationals work in another Member State but do not live there. Because of this crossborder movement of workers, the EU has social security rules that are designed to protect migrant workers from being disadvantaged by working away from home.
The basic principle is one of non-discrimination: migrant workers from another Member State should be treated broadly like other nationals for the purposes of employment, social security, health and other public services. In the absence of any single EU social security system, each country has its own social security and other rules reflecting its particular circumstances, which means in practice that the application of the EU’s principles varies from one Member State to another. EU anti-discrimination provisions benefit the (at least) one million Britons who live elsewhere in the EU and those who are working in another Member State temporarily. It is important to note that the rules refer to migrant workers and their dependants, they do not create unlimited rights to claim benefits or other public services for those not in employment or self-employment."
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