David Cameron has insisted he is planning a "wholly positive" campaign in the EU referendum, after a leaked memo suggested he might seek to play on voters' fears by stressing the risks of a British exit.
Speaking at the conclusion of a European Council summit at which he secured agreement to start talks on renegotiating the terms of British membership, Mr Cameron acknowledged he did not have the backing of all 27 fellow leaders but insisted he was "confident" of reaching a deal allowing him to recommend a Yes vote in the poll, promised by the end of 2017.
Mr Cameron confirmed that Britain would not take any of the 40,000 migrants due to be relocated around Europe under the terms of an agreement reached in the early hours after a fraught meeting which saw Italy's Matteo Renzi accuse counterparts of lacking "solidarity" because of their unwillingness to accept mandatory quotas of refugees.
The Prime Minister signalled deep disagreement with the relocation plan, warning it could be "counter-productive" by attracting more people to travel from troubled regions of Africa and the Middle East in the hope of building new lives in Europe.
Meanwhile, it emerged that the UK will take in over 1,000 vulnerable people a year following the expansion of its contribution to separate UN programmes to resettle refugees who have fled from their home countries, including those affected by conflict or civil war. This is expected to include around 800 Syrians over three years.
Mr Cameron's goal of starting the formal renegotiation of Britain's EU membership took a back seat in Brussels to the Mediterranean migrant crisis and the threat of Greek debt default. The PM addressed fellow leaders on his plans for only five minutes in a break in discussions on migration, and the only response came from Belgium's Charles Michel, who said other EU states must be consulted before final proposals are drawn up.
But Mr Cameron declared himself "delighted" with the agreement that behind-the-scenes talks will begin shortly between UK and EU officials, with national leaders returning to the issue at a Council summit in December.
The Prime Minister briefed all 27 counterparts on his concerns in a bout of whirlwind diplomacy ahead of the two-day summit.
A note detailing one of these private meetings, obtained by The Guardian, suggested that he had told them he has set himself the "firm aim" of keeping the UK in the EU.
The note said he was planning to focus his EU referendum campaign on the "risky" consequences of British exit, after securing promises of reform on welfare for EU migrants, an opt-out from the requirement for "ever-closer union", greater powers for national parliaments and protection for member states which do not use the euro.
The leaked document states that Mr Cameron would like to hold the referendum next year ahead of his self-imposed deadline of December 2017, and suggested he felt the responses from Mr Renzi and German chancellor Angela Merkel were positive, while France was "warier" about free movement and welfare reforms.
The note said: "The PM said that he had deliberately not produced a lengthy shopping list and had been careful in formulating his wish list, but he needed to get satisfaction on these reform demands. He said that he needed to win the middle ground and, if he is to achieve this, then moderate people needed to feel that the things that bother them about the EU have been dealt with."
Ukip leader Nigel Farage said that the note showed the PM's vaunted renegotiation was "a complete con job".
But when he was asked about the document at the conclusion of the Brussels summit, Mr Cameron insisted: "My view is a wholly positive one, which is that I am making positive arguments about how Britain's relationship can change, how Europe can change, so I can make a positive argument about Britain staying in a reformed European Union.
"I have always said, if I don't succeed in that, I rule nothing out."
After fellow EU leaders voiced reservations about his call for treaty change to reform Britain's membership, Mr Cameron acknowledged that renegotiation will be a tough process.
European Parliament president Martin Schulz said there was "quite some resistance" to treaty change, while Estonian PM Taavi Roivas raised the prospect that the move could trigger a wave of referendums across the continent - any one of which could block changes which must by unanimously agreed by all 28 countries.
"Treaty change would probably need referendums all around the EU and that would cause some difficulties as well," Mr Roivas told the BBC.
Mr Cameron said: "I'm not saying that everyone has immediately put up their hands and said `Yes, David, that's marvellous, all these changes. We can nod them through'. They are going to be tough to negotiate, there are some difficult issues to get through."
He added: "Clearly, these talks will take tenacity and patience. Not all the issues will be easily solved. But I'm confident we can achieve a substantial package of reform, for the benefit of Britain certainly, but I would argue for the benefit of the whole of the EU as well.
"Our membership of the EU will once again have a common market at its heart, we will have got off the treadmill to ever-closer union, we will have addressed the issue of migration to Britain from the rest of the EU, we will have protected Britain's place in the single market for the long term.
"It will not be the status quo. We will have fixed problems which have so frustrated the British people. It will be a new and different membership, one that is better for Britain and better for Europe - a membership rooted in what is our national interest today - a Britain in Europe, but not run by Europe."