David Cameron has sought to reassure business leaders that he can secure a "yes" vote in a promised referendum on Britain's membership of the European Union.
The Prime Minister, addressing the CBI conference in London, said he was confident he could secure support for the UK to stay in the EU in the vote which the Conservatives have said they will hold if they win the next general election in 2015.
The CBI published research which, it said, showed that it was "overwhelmingly" in Britain's interest to remain in the EU, with membership worth between £62 billion and £78 billion, around 4-5% of the country's total economic output.
During a question and answer session with business leaders, the Prime Minister insisted his plan to re-negotiate the terms of Britain's membership and then put the new settlement to a referendum before the end of 2017 was not a "short term tactical ploy".
He acknowledged, however, that ministers had not done enough to make the case for the EU but said that he believed the case for a "yes" would be strengthened once reform had been achieved.
"I think that will be a much easier argument to win than the argument we would have if we had an in/out referendum today," he said.
"I sit round that European Union table ... and I can see this organisation is going to change. It is changing in front of our eyes because of the euro. Those countries that are in the euro, they need change to happen.
"We shouldn't stand in their way. But I think it is perfectly legitimate to say 'You, the eurozone members need these changes. Well, we outside the euro, we need some changes too'.
"I think it will be a much more balanced debate because we won't be arguing in/out on the status quo, we'll be arguing about staying in a reformed European Union with a better deal for Britain.
"With the backing of organisations like this one and business voices about the importance of staying a reformed European Union, I think it is an argument we can win."
He added: "We haven't made the argument enough about why Europe matters and frankly there are lots of things in the EU that badly need reform: it is too costly; it is not flexible enough; it doesn't help our competitiveness enough. It needs to change.
"So the argument I have made is not some short-term tactical ploy; it is a long-term strategic choice for Britain."
In its report, the CBI called for a number of reforms, including removing barriers to e-commerce, becoming more outward-looking, and re-focusing the work of EU commissioners.
It said that business also wanted a moratorium on legislation which could be made at national level, and a permanent UK opt-out from the Working Time Directive.
Director general John Cridland said: "We have looked beyond the political rhetoric to examine the pros and cons of EU membership and British business is unequivocal - the Single Market is fundamental to our future.
"But the EU isn't perfect and there is a growing unease about the creeping extension of EU authority. Europe has to become more open, competitive and outward-looking if we are to grow and create opportunities and jobs for all our citizens."
Addressing the conference, shadow chancellor Ed Balls said that leaving the EU would be "reckless, foolish and deeply damaging" for Britain.
"Britain is better placed to shape Europe's future if we are fully engaged rather than having one foot out the door," he said.
"We are clear that there is no future for Britain in walking away from our biggest market - or threatening to do so for reasons of internal party management.
"Europe needs reform, but to walk away from our EU membership would be reckless, foolish and deeply damaging. On Britain's future in Europe, the national interest must come first."