LONDON - Prime Minister David Cameron warned Sunday that Britain would face a “lost decade” if it voted to leave the European Union as Brexit negotiations gummed up the political system.

Cameron is facing a tough fight to keep Britain in the EU in a June 23 referendum. With under two weeks to go, recent opinion polls suggest growing momentum for the “Leave” camp.

In the latest of a string of TV appearances designed to persuade wavering voters to back “Remain”, the premier told the BBC that there could be a “lost decade for Britain” if it votes to leave the European bloc.

“You’ve got to negotiate your exit,” he said. “You’ve got to negotiate a trade deal with the EU.” “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 currently lagging the “Leave” side by 42 percent to 43 percent. A further 11 percent of people surveyed said they did not know how they would vote and 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 average excludes undecided voters.

- ‘Putting two fingers up’ -

“Nobody knows what these polls are saying,” Cameron admitted to the BBC, while stressing he was optimistic of victory.

Meanwhile, the leader of the anti-EU UK Independence Party Nigel Farage told the BBC that the polls showed people were putting “two fingers up” to the establishment.

“Let me just say this: there has been a shift in the last fortnight, there has been a change in this debate,” he 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.”

While Cameron has stressed the economic argument for Britain staying in the EU, the “Leave” camp has repeatedly focused on concerns about the levels of immigration from the EU to Britain.

The possibility of Turkey joining the EU, opening the door to a massive wave of new arrivals, has been a recurring theme.

But 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”. He added: “At the current rate of progress, they will get there in the year 3000”.

Ministers have 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”. “That is completely untrue,” they added.