Prime Minister David Cameron has said Britons could get the chance to vote on leaving the European Union earlier than expected.

Cameron initially pledged to let Britons vote to either leave or stay within the EU via an in/out referendum - dubbed a Brexit - in 2017, provided the Conservative party remains in power after the general election.

However, Cameron hinted that the government could call for the referendum ahead of schedule, if negotiations with the bloc over the EU treaty are successful.

"Absolutely, the referendum must take place before the end of 2017," said Cameron on the BBC's Andrew Marr Show, when asked if a vote could be called earlier than expected.

"If we could do that earlier, I'd be delighted, if we could deliver on this referendum then the sooner I can deliver on it the better.

"What I've said is that if I don't get what I want I rule nothing out and ruling nothing out means just that.

"Let's be clear: in politics you should try and explain what it is you want to achieve, and what I want for my country is to reform the European Union, to make it better, and then recommend that we stay in the European Union because we need those trade links, we need those markets open, we want that influence in the world, that is good for Britain.

"There are Conservative Members of Parliament who want to leave the European Union come what may. But if you're part of the Government then clearly you're part of the team that is aiming for the renegotiation referendum."

In January this year, UK Chancellor George Osborne told the EU that Britain is likely to exit the bloc unless it overhauls its structure and the power it has over its members.

Osborne said: "Our determination is clear: to deliver the reform and then let the people decide.

"It is the status quo which condemns the people of Europe to an ongoing economic crisis and continuing decline. And so there is a simple choice for Europe: reform or decline," he added.

Meanwhile, a Europe Economics report, commissioned by Business for Britain (BfB), has warned that the UK will be forced to join the euro or leave the European Union if the country does not secure "considerable reforms" to the setting of EU financial regulation.

"The changes we need are the changes that are good for Britain and good for Europe," Cameron said on the BBC show.

"They do involve treaty change, and proper, full-on treaty change. We need to get out of ever closer union, that is something that shouldn't apply to the United Kingdom, we need parliaments to be able to combine to block regulations, I think that is very important, we need guarantees that as the single currency gets more countries in it the single market which Britain remains in is properly protected."