David Cameron has warned European leaders that "emotional" ties alone will not keep Britain in the EU, as he set out four "substantial" pillars for his renegotiation.
Fleshing out his reform demands, the Prime Minister said the UK must be exempted from the commitment to "ever-closer union", be allowed to restrict benefits for migrants, get protection from eurozone integration, and see improvements in competitiveness.
Admitting that some people would accuse him of seeking too little, Mr Cameron insisted he was asking for what Britain "needs". He also dismissed the idea that an 'out' vote in the looming referendum on membership would lead to a further negotiation process.
The intervention, in a speech at the Chatham House think-tank, came as Mr Cameron sent a letter to European Council president Donald Tusk spelling out his renegotiation checklist.
Denying that he was embarked on "Mission Impossible", he said: "I have every confidence that we will achieve an agreement that works for Britain and works for our European partners.
"If and when we do so ... I will campaign to keep Britain inside a reformed European Union.
"But if we can't reach such an agreement and if Britain's concerns were to be met with a deaf ear, which I do not believe will happen, then we will have to think again about whether this European Union is right for us.
"As I have said before - I rule nothing out."