David Cameron unveils U.K.'s quest for EU changes ahead of referendum

British Prime Minister David Cameron laid out his government's demands for European Union reform Tuesday, saying a looser "British model of membership" would let him argue that his country shouldn't walk away from the 28-nation bloc.

Cameron said the EU must agree to "irreversible changes" that would cede autonomy back to member states and limit freedom of movement, a key EU principle, by allowing the U.K. to restrict benefits for European immigrants.

Britain will hold a referendum by the end of 2017 on whether to leave the EU. Cameron says he wants to stay in, provided he can secure the reforms he seeks.

He acknowledged that getting the other 27 nations to agree to Britain's goals would be a major challenge but not "Mission: Impossible."

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"I would argue that it's Mission: Possible, but it's going to take a lot of hard work to get there," he said.

The EU's executive, however, called some of the issues raised by Cameron "highly problematic."

Cameron outlined his demands in a speech in London and a letter to European Council President Donald Tusk.

He told an audience at the Chatham House think-tank that his country wants change in four areas, including protection for countries such as Britain that don't use the euro single currency, less red tape and greater power for national parliaments to opt out of rules made by the Brussels-based EU.

"We are a proud, independent nation. We intend to stay that way," Cameron said, stressing that Britain wanted a "clear, legally binding and irreversible" exemption from the EU's commitment to an ever-closer union.

Seeking more immigration control

Most contentiously, Cameron said Britain wants to "control migration from the European Union." He said Britain wants to bar EU migrants from receiving tax credits and other benefits paid to working people during their first four years in the U.K.

In the letter to Tusk, Cameron said Britain's concerns "boil down to one word: flexibility."

He asked for recognition that the EU has more than one currency and that changes made by the 19 euro-using countries such as the creation of a banking union must be voluntary for non-eurozone members like Britain.

He also said British taxpayers should "never be financially liable" for supporting the euro currency.

Some of Cameron's proposals will likely find sympathy in other European capitals, such as his call for fewer regulations on businesses and for more powers for countries within the EU.

He said "the burden from existing regulation is still too high" and that groups of national parliaments should get the power to stop "unwanted legislative proposals" from Brussels.

Cameron's demands on migration are far more problematic.

It is a key EU principle that citizens have the right to live and work in other member states. But Cameron said the level of EU immigration to Britain more than half a million people between 2004 and 2013 was "unregulated and much higher than planned."

Cameron's attempt to limit EU migrants' benefits for four years is likely to be a tough sell with some EU leaders, who see free movement of labor, as well as of goods, as a cornerstone of the bloc.

"We don't want to destroy that principle," Cameron said in his speech. "But freedom of movement has never been an unqualified right."

'Highly problematic'

Margaritis Schinas, spokesman for the EU's executive European Commission, said that some of Cameron's proposals might be feasible, but that others ranged from "difficult to worse."

He said proposals such as the limits to benefits were "highly problematic, as they touch upon the fundamental freedoms of our internal market."

German Chancellor Angela Merkel said she was willing to work with Cameron on his proposals, which contained "no surprises."

"If one has the spirit that we can solve these problems then I'm convinced it can be done," she said.