British prime minister David Cameron argued on Sunday that the island nation is “entitled” to demand changes in its relationship with Europe because countries in the eurozone need its support to deepen economic and fiscal integration among themselves.

In an interview with the BBC’s Andrew Marr, the British leader pointed out that members of the European single-currency union “have got to change to make their currency work.” The United Kingdom needn’t participate in all attempts at closer union. In November of 2011, it refused to sign a fiscal compact that strengthened budget discipline in the euro states. It has refused to participate in bailout schemes for weaker nations in the periphery of Europe. And as most of the continental European states move toward a banking union that centralizes financial oversight in the European Central Bank, Britain might once again opt out.

The members of the eurozone, said Cameron, are “changing the nature of the organization to which we belong” so Britain is “perfectly entitled and not just entitled but actually enabled because they need changes to ask for changes ourselves.”

While the conservative leader promised that voters would be offered a “real choice” on Britain’s future in the European Union in the next election, he cautioned against withdrawing from the body altogether, noting that half of British trade is with other countries in the European Union and London would be unable to help “write the rules” of the single market if it renounced membership.

However, there is strong support for a referendum on membership within Cameron’s ruling Conservative Party. Last year, 81 lawmakers rebelled against party policy and voted in favor of calling such a vote. London’s mayor Boris Johnson, often mentioned as a possible successor to Cameron as party leader, supports a referendum. Meanwhile, Nigel Farage’s right-wing United Kingdom Independence Party now polls higher than Cameron’s coalition partners, the pro-European Liberal Democrats.

According to an opinion survey published in The Times last year, just 32 percent of Britons wants to stay in the single market. 40 percent does not. 27 percent is undecided. Unless a referendum is called in the next couple of years, the parliamentary elections of 2015 will likely be influenced by the question of Britain’s European Union membership.