Next year will be the year when the UK achieves a "fundamental change" in its relationship with the EU and finally addresses concerns about its membership, David Cameron has said.
His comments gave the clearest indication yet that the Prime Minister is planning to stage the in/out referendum he has promised on the UK's EU membership in 2016.
Speaking at the end of a two-day Brussels summit at which he faced resistance from EU counterparts to his plans for changes to welfare rules for migrants, Mr Cameron insisted that "good progress" had been made towards an agreement in February on reforms to the UK's membership.
He has promised to hold the public vote before the end of 2017, but a deal in February would clear the way for the referendum to be held much earlier, with most pundits believing that June is his preferred date.
Mr Cameron made clear that, if the reforms he is seeking are agreed, he will argue in the forthcoming referendum that continued EU membership is good both for Britain's economic security and its national security.
The Prime Minister said: "We've made good progress, we are a step closer to agreement on the significant and far-reaching reforms I have proposed.
"It is going to be tough and there is a lot of hard work to do .
"But I believe 2016 will be the year we achieve something really vital, fundamentally changing the UK's relationship with the EU and finally addressing the concerns of the British people about our membership.
"Then it will be for the British people to decide whether we remain or leave. It is a choice we will all need to think hard about.
"I believe if we can get these reforms right - and I believe that we can - I firmly believe that for our economic security and increasingly for our national security, the best future for Britain is in a reformed European Union."