David Cameron has held out the prospect of a referendum on Britain's relationship with the European Union - but only when it has been "fundamentally" changed.
The Prime Minister dismissed the idea of an immediate in/out referendum, insisting that would be putting a "false choice" in front of voters.
But he said he is "not against a referendum" altogether and is in favour of one "in some cases".
"The principle, I think, should be this: if you are fundamentally changing the relationship between Britain and Europe, then you should be having a referendum," he told BBC Radio 4's Today programme.
Asked whether it should be a straightforward question of in or out, Mr Cameron said he would set out more detail in a highly anticipated speech on the subject he is due to deliver in the Netherlands this month. "You will have to wait for the speech for the full details but obviously I want to give people a proper choice," he said.
"What I don't favour, I think if we had an in/out referendum tomorrow or very shortly, I don't think that would be the right answer for the simple reason I think we would be giving people a false choice, because right now there are a lot of people who are saying I would like to be in Europe but I'm not happy with every aspect of the relationship so I want to change. That is my view, so I think an in/out referendum is a false choice."
Amid claims from some in his party that it might be in Britain's interests to leave the EU, the Prime Minister said: "I'm in favour of our membership of the European Union and I'm optimistic and confident that we can achieve changes in the European Union to make sure that Britain feels more comfortable with our relationship with Europe. I'm confident we can do that."
The Prime Minister dismissed warnings that question marks over Britain's position in the EU are damaging for business, insisting that the debate is unavoidable.
"Europe is changing and the opportunity for us to lead those changes and make changes that make our relationship with Europe more comfortable, I think, are absolutely there, so I'm confident we can do that and then, as I say, a fresh settlement, and then fresh consent for that settlement, I think that's the right approach," he said.
"Those who say this is very dangerous, you are putting at risk the relationship with Europe, you are putting at risk our position with regard to business, I don't agree with that, because this debate is happening anyway."