UK support for staying in EU is wafer thin, says Cameron
British people's support for staying in the European Union is currently "wafer thin", David Cameron has said.
The prime minister argued that his promise to renegotiate powers with Brussels before holding an "in-out" referendum had the "overwhelming support" of the public.
He told business leaders the argument for remaining in the EU could be won if there was substantial reform.
Labour is warning that the UK could "sleepwalk out of the EU".
But Sir Michael Rake - president of the CBI business group - has warned both the Conservatives and Labour against political posturing on Europe and other issues, including energy prices, immigration, and the HS2 rail project.
"It is very important that politicians, across the board, are careful about the words they use and the policies they espouse because this can lead to prejudicing investment and careless words can cost jobs," he told the BBC.
Mr Cameron has promised to hold a referendum on whether the UK should quit the EU by the end of 2017 if the Conservative Party wins a majority at the next general election.
This, he says, would follow a fundamental renegotiation of the relationship between London and Brussels.
Speaking at the CBI's annual conference, Mr Cameron said: "The current consent for remaining inside the European Union is wafer thin. We haven't made the argument enough about why it matters."
He added: "The argument I have made is not some short-term tactical ploy. It's a long-term strategy for Britain."
Mr Cameron also said: "What I've put forward, I believe, has the overwhelming support of the British people and business people too."
The CBI has published a report saying the EU is worth between 4% and 5% of UK annual output and is "overwhelmingly" best for business but that reforms are needed.
The prime minister described the findings as "hugely helpful" to the European debate, adding: "The trouble is that the debate was just slipping away."
He added: "We are doing what the British people and, I think, most business want. Let's get in there and negotiate a better deal for Britain. Then let's put the question."
Mr Cameron said it was not for the UK to "stand in the way" of further political and financial integration by members of the eurozone, but it was "perfectly legitimate to say we outside the euro need some changes too".
For Labour, shadow chancellor Ed Balls told the conference that the UK was "better placed to shape Europe's future if we are fully engaged rather than having one foot out the door".
He added: "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."
The CBI has said uncertainty about the outcome of a future referendum is already having a negative impact on inward investment.
But the UK Independence Party said the CBI's view that leaving the EU "would somehow mean a sudden end to trading with Europe" was "deeply flawed".
"The CBI does not consider the more realistic option that if we left the single market and freed ourselves from its red tape and politicised agenda we would still be able to continue to trade strongly with Europe on our own terms," said the party's leader Nigel Farage.
"Leaving the EU would not mean turning our back on Europe."