The likelihood of the U.K. exiting the European Union (EU) currently stands at 50 percent, with the next flashpoint in May next year, according to new research.
Britain's future in the EU has been a matter of intense debate over the past 18 months, culminating in the announcement by Prime Minister David Cameron that there would be a referendum on membership in 2017, if his Conservative Party is in power. This followed the eruption of the euro zone debt crisis, and pressure from his own party members over the U.K.'s perceived loss of some powers to Brussels.
Alastair Newton, senior political analyst at Nomura, reiterated his view that the chance of Britain exiting the EU – a so-called "Brixit" - was 50 percent in a research note Thursday, but said there were still uncertainties.
"We foresee events in the next 12 months which could cause us either to increase or to decrease this probability but without being decisive," he wrote.
The European Parliament elections in May 2014 will be one of the key events which will determine the country's future membership of the European body, he argued, adding: "We now think it more likely that it will be at least 2015 and possibly even 2016 before a clearer picture emerges. But what is clear is that this is not a topic which is about to go away."
(Read more: Could Brixit be next problem for EU?)
Growing support for the Eurosceptic U.K. Independence Party (UKIP), led by Nigel Farage, was one of the key factors which spurred Cameron into announcing a referendum, and Newton believes the party will put in a strong performance next year.
This could put further pressure on the opposition Labour Party to commit to holding a referendum if they get into power.
But the minority party UKIP may find its popularity slipping, with renewed focus on its representatives. Godfrey Bloom, a UKIP Member of the European Parliament, described countries which receive U.K. foreign aid as "bongo bongo land" in a speech last month – a term condemned by many as racist.
(Read more: How Brixit could affect U.K. economy)
The referendum itself may never happen, as it is dependent on either the Conservative Party winning an overall majority at the next election, or being part of a coalition government that is willing to back a referendum.
There is also no certainty over which way the British electorate would vote, even though a noisy minority are anti-EU. There are a hefty proportion of undecided voters in polls on EU membership at the moment, who could be swayed by ongoing developments and renegotiations of the U.K.'s relationship in the EU.