Agreed. The British reaction to this influx, I suspect, won’t be very positive.

I suspect that the biggest migration pressures will be introduced when Romania and Bulgaria get admitted to the European Union. There’s been non-trivial levels of out-migration from those two poorer countries–apparently Bulgarians already play in the Greek economy much the same role as Mexicans in the Californian economy, to say nothing of the porosity of the Romanian-Moldovan frontier.

Furthermore, most people don’t want to leave home. People imagine that immigrants make careful wage calculations and go whenever the money is better. This is rarely the case. Expatriation has enormous costs, both financial and personal, and few unskilled people will do it unless they feel things are not only better elsewhere, but bad at home. There are some adventurous - and usually skilled - workers who will just take opportunities abroad without worrying too much about it, but they’re the ones you probably wish to encourage.

No, there will be no flood of workers into Germany when the restrictions disappear, and there wouldn’t be any if the restrictions weren’t in place. The UK will not find itself flooded with Eastern European immigrants, except for the Roma, for whom eastern Europe does suck and anything in the UK really is better.

People like to think about deadlines, and the 1st of May acts as a symbolic milestone. One month after the new member states have joined governments will be able to start lifting restrictions and no-one in the press will notice.

The large gaps in income and unemployment between Prague and the rest of the Czech Republic, or Budapest and the rest of Hungary, or even (to a certain degree) between the Warsaw area and the rest of Poland haven’t created much internal migration, this is true.

That said, there has been substantial migration within, from, and to central Europe after Communism. Magyar immigration to Hungary from Romania and Slovakia, the sorting-out of ethnic minorities in the former Yugoslavia, and a small drift of Slovaks to the richer Czech Republic after Czechoslovakia’s end are examples of the first sort of international migration; immigration by nominal ethnic Germans (especially from Poland) to Germany and temporary migration by central Europeans to Germany and Austria are examples of the second sort of international migration; long-distance migration to central Europe by Chinese, Vietnamese, Ukrainians, Armenians, and Russians constitute examples of the third sort of international migration.

Will central Europe empty out starting in May? Very unlikely. Will international migration increase? Probably, yes, given that income gaps between (say) Germany and Poland now are substantially greater than between France and Spain in the mid-1980s, while levels of human development are broadly comparable. Will this migration be a bad thing? Not for the receiving countries, and hopefully not for the sending countries.

Will this migration be welcomed? Probably not. All Europeans–and not only those living in the EU-15–are fairly hostile towards immigration. This is a shame, but given the greater hostility towards immigration now as opposed to two decades ago, repeating the Spanish/Portuguese deal was likely the best that could be hoped for.

Contra this, the migrational potential from many of the member-states seems to be substantially larger. Poland, I suppose, is particularly important given its relatively low level of economic development, though once Romania and Bulgaria join it will be quickly surpassed.

The Czech Republic, Slovakia, Hungary, and Slovenia appear to be net receivers of immigrants now, based on relatively high levels of economic development and economic structures conducive to immigration. Possibly these countries–along with the Baltics?–might have the restrictions lifted early?