Brexit: Britons Who Support Leaving EU Ahead in Polls Amid Warnings From Economic Leaders

Latest poll shows more Britons support leaving the European Union.

Cameron has appeared increasingly uneasy ahead of the June 23 referendum, as the latest official poll by YouGov/GMB gave a slight majority to the pro-Brexit camp -- 45 to 41, with 11 undecided and a small fraction of people saying they would not vote.

The director general of the World Trade Organization told The Times, “It could be a few years, it could be decades," for new trade deals with the U.K. to be negotiated, adding that to expect "smooth sailing and quick results would be a high-risk bet."

Cameron urged voters to get involved.

“Don't stand on the sidelines. This matters for you,” he said. “There are no second chances, no re-runs."

"The safer choice is voting to leave, so we can take back control of our money, borders, security, trade and taxes," Johnson said in a joint statement with other pro-Brexit officials. "We think that the public deserve the chance to hear these issues debated face-to-face between the prime minister and a spokesman for Vote Leave so they can judge for themselves which is the safer choice on 23 June."

In terms of latest polls, a majority of the population in other European countries polled believe it is likely that more countries will choose to leave the E.U. in the event of a Brexit.

Results could depend on whether people aged 18 to 24 stay at home in similar numbers as for the general elections, when only four in 10 voted, according to analysis by the Press Association.