Prime Minister David Cameron on Wednesday promised to make it harder for migrants from the European Union to access Britain's welfare system and pledged to try to restrict the freedom of movement of people from poorer EU states in time.
His plan, an attempt to address public fears about an influx of Romanians and Bulgarians when EU restrictions on those two countries expire next year, drew a rebuke from the European Commission which said his intervention was "an unfortunate over-reaction".
But Cameron, whose Conservative party risks seeing its vote split at European elections next year and at a national election in 2015 by the anti-immigration UK Independence Party, is under pressure to act at a time when he is trailing in the polls.
He has said he will try to renegotiate Britain's membership of the EU to give it more of a say over its own affairs and has promised to hold an in/out referendum if re-elected in 2015 amid public scepticism about the benefits of belonging to the bloc.
"The EU of today is very different from the EU of 30 years ago," Cameron said in an article in the Financial Times.
"We need to face the fact that free movement has become a trigger for vast population movements caused by huge disparities in income. That is extracting talent out of countries that need to retain their best people and placing pressure on communities."
Cameron said he planned to change British law so that new EU migrants would have to wait three months before they could access unemployment benefits, saying he shared deep public concerns about a possible influx of new migrants.
Newcomers would not be eligible for housing benefits and would lose the right to unemployment benefits after six months unless they could prove they had a realistic chance of finding a job.
He said he also planned to try to renegotiate the way EU freedom of movement rules are applied to make it harder for people from poorer countries in the 28-nation bloc to relocate to richer countries in time.
That, he said, could involve capping the annual number of EU migrants or withholding full freedom of movement rights until a country achieved a certain gross domestic product per head.
"Britain, as part of our plan to reform the EU, will now work with others to return the concept of free movement to a more sensible basis," he wrote.
"We must put in place new arrangements that will slow full access to each other's labour markets until we can be sure it will not cause vast migrations."
The previous Labour government waived transitional controls for migrants from new EU members states, something Cameron called a "monumental mistake" which meant 1 million people from central and Eastern Europe were now living in Britain.
Laszlo Andor, the European Commissioner for Employment and Social Affairs, said the kind of "unilateral rhetoric" Cameron was indulging in on immigration was unhelpful.
"This is an unfortunate over-reaction. We would need a more accurate presentation of the reality, not under such hysteria which sometimes happens in the UK," he told BBC radio.
"Unilateral rhetoric ... is not really helpful. It risks presenting the UK as a kind of nasty country. We have to look into the situation collectively and act proportionately."