London (AFP) - Prime Minister David Cameron warned Sunday that Britain faces a "lost decade" if it leaves the EU, as he races to persuade undecided voters less than two weeks before a close referendum.
With several recent opinion polls suggesting momentum is with the "Leave" camp, Cameron is making a string of television appearances to try to convince people to back "Remain" on June 23.
A string of global institutions including the International Monetary Fund (IMF) and G7 have backed Cameron's argument that Britain's economy would be damaged by Brexit.
But "Leave" supporters argue that Britain could thrive outside the EU, where they say it would be freed of red tape.
One of the leading pro-Brexit campaigners, UK Independence Party leader Nigel Farage, said that voters were putting "two fingers up" to establishment figures like Cameron.
The prime minister told the BBC on Sunday that there could be a "lost decade for Britain" after a vote to leave the EU as the political system gets gummed up with negotiations.
"I think we'd be looking at a decade of uncertainty," he added. "It would suck the energy out of our government and our country."
A Sunday Times/YouGov online poll found that Cameron's "Remain" campaign is lagging the "Leave" side by 42 percent to 43 percent.
Eleven percent of people surveyed said they did not know how they would vote, while four percent said they would not take part in the ballot.
Averaging out the last six opinion polls, both sides are tied on 50 percent, according to academics at the What UK Thinks project. Their figures exclude undecided voters.
- 'Putting two fingers up' -
"Nobody knows what these polls are saying," Cameron told the BBC, while stressing he was optimistic of victory.
But Farage insisted that they showed a real movement towards his side.
"There has been a shift in the last fortnight," the UKIP leader said.
"People have had enough of being threatened by the prime minister and the chancellor and I think collectively people are beginning to put two fingers up to the political class."
The "Leave" camp has repeatedly focused on concerns about immigration from the EU to Britain and the possibility of Turkey joining the bloc.
Cameron dismissed this as a "complete red herring" in Sunday's BBC interview, insisting: "There's no prospect of Turkey joining the EU in decades".
Ministers have also denied a story in this week's Sunday Times that British diplomats had considered letting up to 1.5 million Turkish citizens have visa-free travel to Britain.
The paper published details of five diplomatic documents which it said could mean a planned deal giving Turkish citizens easier access to the EU's Schengen area being extended to Britain.
The EU agreed in March to offer Turkey visa-free access, increased aid and speeded up accession talks in return for Ankara controlling the flood of migrants crossing into Greece.
But in a joint statement, Britain's Home Secretary Theresa May and Foreign Secretary Philip Hammond said "selectively leaked quotes" had been used "to give a completely false impression that the UK is considering granting visa liberalisation to some Turkish citizens".
Meanwhile, WikiLeaks founder Julian Assange told ITV television he was "pretty much" in favour of leaving the EU.
Assange, holed up in Ecuador's embassy in London to avoid extradition to Sweden for questioning over a rape allegation which he denies, said the EU was bad for Britain "because it permits a lack of democratic accountability".