British Prime Minister David Cameron and European Union President Donald Tusk extended talks aimed at reaching a finalized reform deal by the European Union (EU) summit at the end of February.

"There is more hard work to be done," Cameron's spokeswoman told reporters in London on Monday. "We are making progress but there's more work to do in all four areas - more work in some areas than others." Confirmation followed soon after from Tusk's office: another night of overtime was in the offing, the EU would unveil its proposal for reform on Tuesday.

Telling talks, or window dressing?

The Conservative prime minister in Britain is seeking four so-called baskets of reforms, with the fourth - a bid to limit welfare eligibility for EU migrants in the UK - broadly seen as the most contentious. Officially, Cameron's own EU decision, whether he'll campaign to remain in the bloc or leave it, rests entirely on the outcome of these negotiatons.

"I'm a bit hesitant to give the renegotiation too much weight, the reason being that the changes Cameron can secure are relatively minor," Christian Odendahl, chief economist at the Centre for European Reform think tank in London, told DW. "I think the results of the renegotiation matter only insofar as they can be portrayed as a success. Cameron and his advisers will of course claim that he has secured a good result, while the die-hard euroskeptics will say the opposite."

Therefore, Odendahl says he's not convinced that Cameron truly remains Britain's most prominent undecided voter. "He has to say that - first of all as a bargaining chip in negotiating with the EU, but also in terms of increasing public support of his approach to the referendum."

'Remain' campaign leading, but losing ground

Two telephone polls published last week, from Ipsos Mori and ComRes, found that just over 50 percent of participants currently planned to vote to remain, while just over 30 percent favored a so-called "Brexit," with the remainder currently undecided. However, Ipsos Mori's head of political research, Gideon Skinner, warned that these numbers remain finely poised, and subject to swings between now and a potential June referendum.

"Our most recent poll has shown a narrowing in the lead, to the lowest since 2012, when the 'outs' were in the lead. And we know if we look at our long-term trends, it can be volatile. Views can change on this, and there are so many details left to iron out," Skinner said.

"Interesting" amongst the January figures, for Skinner, was the finding that four in 10 voters - on both sides of the divide - still said they might change their minds prior to the vote. Furthermore, the numbers also hinted at pessimism about the talks themselves: "Only about one in three members of the public say they're confident that Cameron will get a good deal in negotiations with other leaders," Skinner explained. "Similarly, only around about 20 percent say that Cameron will achieve most of his goals in the negotiations."

Recent online polls, Skinner said, had delivered stronger results for the 'out' camp; Ipsos Mori noticed an undesirably high participation rate among euroskeptic UKIP supporters in these surveys.

Immigration tops domestic concerns

UK voters famously tend to place their political priorities rather closer to home than Brussels or Strasbourg. Even now, "the EU" only registers as voters' fifth most important issue of the moment, with the perennial frontrunner - migration - topping the list of concerns. This did not escape the attention of opinion-makers on Monday, including probably the most powerful of them all in the private British press:

Still, the EU has not scored so highly among voters' priorities since the summer of 2005, just after people in France and the Netherlands rejected a new EU constitution, and as many British voters complained that they had no such referendum in which to offer their opinion. Could this growing interest, coupled with what's sure to be a fiery domestic campaign, prompt turnout and participation akin to Scotland's remarkable tally of almost 85 percent in the 2014 independence referendum?

"I would be surprised, pleasantly surprised to see turnout as high as it was for the Scottish referendum, where we know there was really intense interest, and obviously on a topic that was absolutely crucial to people living there," Skinner says. He adds he believes turnout should at least eclipse those of European elections: a safer prediction given that a meager 35 percent of eligible Brits hit the polls in May 2014.

Political lay of land, threats on campaign horizon

In UK party political terms, the landscape's relatively simple. A large majority of Labour MPs should support EU membership, most likely along with the Scottish National Party and the few Liberal Democrats left in parliament. Euroskeptic party UKIP will put up a united "leave" front, with the open question being just how many of Cameron's Conservatives decide to campaign on the same side - presumably against their prime minister.

As to which political developments might sway wavering Tories, or indeed those on Labour's more protectionist left, economist Odendahl posits that Europe's refugee influx is more likely to put off voters and politicians than a renewal in Greek debt difficulties.

"The refugee crisis is probably the bigger issue. We don't know how it will escalate - politically escalate - in Europe over the coming six months," Odendahl says. "I don't think it contributes positively to Britain's prospects on staying in, because if the EU is perceived as unsafe from a migration perspective, then that certainly helps the 'out' campaign."

As for influences that might propel the 'in' crowd, Odendahl sees the answer on the markets and in the City of London's crucial financial sector. Asked why Cameron's government seems keen on a 2016 vote, when the prime minister gave himself a deadline through the end of 2017, he said that one goal was to avoid holding the vote in the so-called "mid-term slump," when incumbent governments tend to be at their least popular among the electorate.

"The second question is what does the current uncertainty around Brexit and the referendum do to the UK economy, do to the British pound and so forth. It's an economic risk," he says. "So the longer you wait, the more this economic risk can take effect. For instance, the British pound has weakened considerably recently, which is not easy to explain economically without some kind of extra perceived risk we've not yet factored in - such as the risk of Britain leaving the European Union."