A referendum on Europe would be the "cleanest, neatest, simplest and most sensible" way of resolving question marks over Britain's future in it, David Cameron has insisted.

The Prime Minister's comments left no doubt that the Tories will propose a poll after the 2015 General Election on a renegotiated settlement for the UK.

With fears rising at Conservative headquarters that UKIP, the anti-EU party, could pose a serious threat to some Tory seats at the next election, the Prime Minister is coming under increasing pressure to placate his party on Europe, particularly the Eurosceptic rightwingers.

However, he has ruled out an in-out referendum.

He said: "Europe is changing. The eurozone is going to integrate, they are going to do more things together and that's right for them and it's necessary if they are going to save the single currency.

"But that does give the opportunity for Britain to get a fresh and a better settlement with Europe and I'm committed to making sure we do everything to set that out in the run-up to the next election, to get that fresh settlement and then seek fresh consent for that settlement.

"I want to change the status quo.

"We have always said when we achieve that fresh settlement, it needs consent either at a referendum or a general election.

"A referendum is obviously the cleanest, neatest, simplest and most sensible way of doing that. But it is right to leave open that question for the time being."

Mr Cameron said the first priority for Europe was resolving the eurozone crisis and Britain must show strategic patience before raising its own questions.