David Cameron has promised that voters will be given a "real choice" about Britain's future relationship with the European Union.
The Prime Minister is set to make a key speech on the UK and Europe later this month amid pressure to call an in-out referendum on future membership.
Mr Cameron refused to be drawn precisely on how he would respond to mounting euroscepticism but promised it would be substantial.
Concerns over the electoral threat of UKIP, which is enjoying record opinion poll ratings and had significant support at recent by-elections, are fuelling Tory demands for a radical policy.
"It will demonstrate very clearly that it is the Conservative Party at the next election that will be offering people a real change in terms of Europe and a real choice about that change," he said.
The Prime Minister is expected to use the long-delayed speech to set out proposals to negotiate the return of powers from Brussels and allow a public vote.
Speaking to BBC Radio 5 Live, he admitted any renegotiation would be "tough" but insisted Britain is better off staying in a reformed EU than pulling out completely.
"I don't think it's right to aim for a status like Norway or Switzerland where basically you have to obey all the rules of the single market but you don't have a say over what they are," he said.
The president of the European Council, Herman Van Rompuy, has warned attempts to claw back powers from Brussels would put the future of the single market at risk.
Cherry-picking policies would see the union "unravel", he suggested.
But Mr Cameron said it was "perfectly legitimate" to seek to use the EU's need to reform and shore up the ailing euro to reshape Britain's membership.
The Prime Minister has also faced criticism from his Liberal Democrat deputy Nick Clegg, who has called for Britain to have the confidence to take the lead in Europe.
Mr Clegg, a renowned europhile, branded plans to repatriate powers a "false promise wrapped in a Union Jack" and said talk of a referendum was no more than "political shadow boxing".
"They do not really want to change any aspect of our relationship with Europe," Mr Cameron said of his power-sharing partners in government.
"The coalition is, I think, performing very well but of course there are some areas where we do not agree and Europe is one of those."
UKIP leader Nigel Farage claimed Mr Cameron was "begging at the top table" in Brussels for small changes.
"No matter what he says now, after so many broken promises, so many 'cast-iron guarantees', can anybody honestly believe that he will be telling the truth this time?," he said.
"The simple fact is that he wants us to stay in the European Union no matter how it is configured."
Mr Farage continued: "Mr Cameron says that he will offer a real choice in 2015. That choice exists already.
"Voters can support one of the three old parties, including the Conservatives that want to keep us tied down by Brussels and its regulations, or they can opt for UKIP, which gives a clear commitment to withdraw."