British voters should be given a referendum on the country's membership of the European Union, said the leader of the Green Party.
Conservatives are promising voters an EU referendum in 2017 if they win the upcoming general election.
They are trying to stem the haemorrhage of Tory voters to eurosceptic Ukip, which won the European Parliament elections in May and two subsequent by-elections triggered by defectors from the Conservatives: Douglas Carswell in Clacton and Mark Reckless in Rochester.
But Labour, which is also losing part of its support base to Ukip, has only gone as far as saying it would hold a referendum if more powers were transferred from Westminster to Brussels.
"We support a referendum because we believe in democracy," Natalie Bennett, leader of the Green Party, told IBTimes UK in a wide-ranging interview.
"We trust in the voters. You have to be in your late fifties to have had any chance to vote on Europe. We wouldn't have necessarily started calling for it, but now it's on the table we say fine. Let's trust the voters."
Bennett said she would urge Labour leader Ed Miliband to commit to an in/out referendum if his party wins the election: "But I think given Miliband's track record on most things, continuing to sit on the fence is the most likely Labour position."
There has been disquiet for years in British politics about the EU, which critics say is undemocratic and erodes national sovereignty.
Proponents argue it is a huge market of 500 million citizens and so the British economy is better off by being inside where it can influence the rules and trade freely.
One of the fundamental pillars of the EU is the free movement of people.
Since the early 2000s as the 28-member EU incorporated poorer central and eastern European states, the UK has experienced mass immigration.
Many Britons perceive themselves as worse off as a result. They believe they face more competition for jobs, housing, schools and healthcare.
But academic research has concluded that immigrants from the EU contributed billions of pounds more into the system than they take out in the form of welfare and public services.
Ukip has won favour over its hawkish stance on immigration and leaving the EU.
Despite pledging an in/out referendum, Tory Prime Minister David Cameron wants to stay in the EU. But he also wants reform and is trying to claw back powers from Brussels.
He is currently lobbying fellow leaders for a tightening of the free movement of labour rules, including temporary restrictions on the number of EU migrants entering the UK.
But he is convincing few. German Chancellor Angela Merkel, the most influential leader in Europe, has said there is no room for negotiation over the free movement of labour.
An official in Merkel's office was quoted by Der Spiegel as saying: "Should Cameron persist, Chancellor Angela Merkel would abandon her efforts to keep Britain in the EU."