'More work' needed in Brexit talks as polls hint UK to stay in EU

"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."

...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."