– Prime Minister David Cameron said he's confident about his campaign to keep Britain in the European Union as he reiterated his core message that leaving would damage the economy.

Cameron, speaking on BBC, rejected accusations by Independence Party Leader Nigel Farage that the campaign to keep Britain in the E.U. has been based on scaremongering. Still, both Cameron and Chancellor of the Exchequer George Osborne published warnings in Sunday newspapers that leaving the E.U. would threaten state pensions and the National Health Service. Britons will vote on the matter on June 23.

"If we vote out, there will be a decade of uncertainty," Cameron said. "There's no saving from leaving the E.U.; there's a cost. I guess my message is very clear, which is, don't risk it."

The push to leave the E.U. has gained momentum as campaigners focus on immigration, suggesting the government's message on the economic consequences isn't getting through to voters. Both sides have been accused of misrepresenting the facts, while campaigning continues to split the Conservative party.

"I don't want us to take the risk with our economy," Cameron said. "I'm confident we have the strongest and the most positive case. Nobody knows what these polls are saying."

He acknowledged that a vote to leave would have "consequences which will be very difficult for the government to deal with," though he said he would remain as prime minister.

Many voters are still undecided. An online survey by Opinium for the Observer newspaper showed 44 percent support Britain remaining in the 28-nation E.U., up from 43 percent a week ago. Forty-two percent of respondents backed leaving the E.U., also up 1 point from the poll released on June 4.

In Saturday's Opinium poll, 13 percent of the 2,009 U.K. adults surveyed said they didn't know if the nation should stay or go. When pressed, though, about 38 percent of the undecideds were leaning toward "Remain" and 25 percent toward "Leave" — suggesting that late deciders could tip the balance in favor of staying.

Farage rejected the possibility of a second referendum should the vote result in a narrow win to remain in the bloc.

"A vast majority of our political class want to stay part of the E.U.," Farage said. "If the leave side was to narrowly lose, the chances of parliament giving us a referendum" in the future are "probably pretty slim."