Kirsty Wigglesworth / Pool / AP

Prime Minister David Cameron, in a letter to the president of the European Council, is seeking an overhaul of the European Union ahead of a U.K. referendum in 2017 over whether to remain in the bloc.   

“This is perhaps the most important decision the British people will have to take at the ballot box in our lifetimes,” Cameron said in a speech at the Chatham House think tank in London.

The U.K. is seeking an overhaul of four areas:

Economic governance: Britain is one of nine EU members that’s not part of the eurozone, the group of nations that uses the single European currency, the euro. Cameron says he wants to ensure Britain isn’t discriminated against economically because it’s retaining the pound. Here’s more from his letter to Donald Tusk, the EC president:

Competitiveness: Cameron says he wants the EU to make it easier to do business across the bloc. In the letter, he says the “burden from existing regulation is still too high,” and the U.K. “would like to see a target to cut the total burden on business.”

Sovereignty: This is perhaps the most important of Cameron’s demands, and one that Euroskeptics in the U.K. will be watching closely because they believe the country’s membership in the EU erodes its sovereignty.

In addition, Cameron wants national security to remain the sole responsibility of member states, “while recognizing the benefits of working together on issues that affect the security of us all.”

Immigration: This is another concern in Britain because the bloc allows for free movement of all of the EU’s citizens, and Britons worry that the EU’s newer—and poorer members—will burden the country’s schools, hospitals, and public services. The population of the U.K., Cameron noted in his letter, is already expanding, and it’s set to become the bloc’s most-populous country by 2050. At the same time, he says, net migration is 300,000 a year.

“That is not sustainable,” Cameron wrote in his letter to Tusk. “We have taken lots of steps to control immigration from outside the EU. But we need to be able to exert greater control on arrivals from inside the EU too.”

In response, Tusk tweeted:

Britons will vote in what’s being called an in-out referendum by the end of the 2017. Polls show that membership in the EU, once unpopular, has gained support in recent years.

Still, the EC might find some of Cameron’s demands unpalatable. Here’s Margaritis Schinas, the EC spokesman:  

Prima facie we see a number of elements which appear to be feasible, like finding ways to increase the role of national parliaments, some issues which are difficult, like ever closer union and relations between the euro ins and outs, and some things which are highly problematic as they touch upon the fundamental freedoms of the internal market. Direct discrimination between EU citizens clearly falls into this last category.

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