DAVID Cameron has admitted his bid to reform Britain's relationship with Brussels was "not met with a wall of love" when he met his European counterparts in Latvia but he nonetheless insisted he was confident of success and pledged patience and tenacity in achieving it.

The Prime Minister's Euro charm offensive will gain momentum next week when he meets Jean-Claude Juncker, President of the European Commission, at his country retreat of Chequers on Monday and will travel to Paris and Berlin for talks with President Francois Hollande and Chancellor Angela Merkel.

During an eastern European summit in Riga, national leaders expressed concern that as the referendum debate progressed in Britain that Mr Cameron might lose the momentum in a surge of nationalism as happened in the Scottish independence poll.

One summit source said there was "a risk" that, just like last September, a comfortable lead could evaporate and a knife-edge result might follow. "You only have to look at Scotland," he added.

The PM again refused to ruled out campaigning for Britain to leave the EU if his renegotiation efforts failed and said it would be "good" if the popular vote could be staged earlier than his 2017 deadline. The Herald revealed earlier this week that the UK Government's EU Referendum Bill would take priority in the Queen's Speech, leading to speculation that the Conservative leader was preparing for a referendum next year, 12 months earlier than originally planned.

After a series of one-to-one meetings with EU leaders, Mr Cameron told reporters he would not "negotiate in public" but said there had been a "reasonable start" to today's discussions and the sooner reforms were made, "the better".

He pledged that his mission for reform would be "constant" and warned "there'll be lots of noise, lots of ups and downs along the way".

Asked whether or not he could campaign for the UK to leave the EU, the PM replied: "I'm confident, I've set out a series of changes which address the main concerns, which the British people have, that I have about Europe and the way it works and I'm confident of getting those changes.

"I've tried to aim at things that are deliverable and doable rather than things that are impossible. But I've always said that if I don't get what I think I need, I rule nothing out."

Mr Cameron admitted his presence at the summit had been met with a less than enthusiastic reception by some.

"On the irritation factor, I'm not going to say I was met with a wall of love when I arrived but there were lots of people who were very excited about our election result and congratulated me and we all said how much we are looking forward to working together."

Britons, he stressed, were "not happy with the status quo" but he said he believed "we can transform our relationship with Europe for the better; I don't expect to find agreed solutions straight away".

He added: "These talks will require patience and tenacity but by working together in the right spirit and sticking at it I believe we can reform the EU and our relationship with it. And then the British people will have the final say; they will decide."

EU leaders in Riga were broadly positive, with Finnish premier Alexander Stubb expressing confidence that a deal could be found which would satisfy all sides.

"Finland is very much in favour of the pro-reform agenda that David Cameron drives. We believe that there are issues that can be discussed with Britain."

Estonian prime minister Taavi Roivas said he was "open to discussion" but warned that he would oppose any attempt to roll back the free movement of labour within the EU.

Meantime, President Hollande made clear it was up to Britain to make the necessary effort if it wanted to push through change, saying: "We ask for nothing. Europe is not concerned by a vote."

Meantime, Alex Salmond was accused by Labour of "staggering hypocrisy" after admitting that he could stand alongside Conservatives in the bid to keep the UK in the European Union.

Asked if he would share a platform during the Euro campaign with Chancellor George Osborne, the former First Minister replied: "Listen, I share platforms with everybody except fascists and non-democrats."

Given the Gordon MP ferociously attacked Labour for working alongside the Tories in the No campaign during the independence referendum, Jackie Baillie for Scottish Labour hit back, saying: "Alex Salmond's hypocrisy is staggering. After years spent attacking the Labour Party during the referendum, he is now jumping into bed with the Tories on the EU referendum."