Iain Duncan Smith has said the campaign for Britain to leave the European Union may "carry the day", as David Cameron steps up his efforts to renegotiate the UK's membership.
The work and pensions secretary is seen as one of the more eurosceptic members of Cameron's cabinet. He widely seen as most likely to prefer to quit rather than be forced to campaign for Britain to remain a member of the EU.
Speaking in the Commons on Monday, Conservative MP Philip Davies told Duncan Smith: "The only way this country will get complete control over benefits policy for EU citizens is by leaving the EU."
The work and pensions secretary replied: "The prime minister has given the country a referendum on that matter which is a huge step forward.
"I suggest that moment he is able to make that powerful argument I am sure no doubt under his rhetoric he may yet carry the day."
Last week Cameron gave his most pro-EU speech since committing himself to hold a referendum. He warned voters that life outside the union would not be a land of "milk and honey".
Today, George Osborne will meet with German finance minister Wolfgang Schauble in Berlin. The chancellor has said the British and German economies are the "beating heart" of Europe ahead of the talks which will focus on reforming Brussels.
Securing backing from Germany is crucial to the success of the plans to renegotiate Britain's relationship with the EU and David Cameron has keenly courted support from Angela Merkel.
Osborne said: "Together we make the world's third-largest economy, behind only America and China and since the crisis ended, we have generated two-thirds of EU growth.
"But the future holds challenges for our economies. We must cut debt and boost productivity. To do this, we need a strong EU, fit for today's challenges and working for the benefit of all 28 member states.
"The UK's reform and renegotiation plans aim to achieve this, which is why these talks with key partners in Europe are so important."