Svenja O’Donnell writes at Bloomberg:

British public opinion is too close to call on whether the country should stay in the European Union, with many voters still undecided as interest groups and political leaders make their cases, according to an Opinium survey released on Saturday.

The poll for the Observer newspaper showed 44 percent support Britain remaining in the 28-nation bloc, up from 43 percent a week ago. Some 42 percent of respondents backed leaving the European Union, also up 1 point from the previous poll released on June 4, as attitudes start to crystallize ahead of the June 23 referendum, but the differences aren’t statistically significant.

Earlier on Saturday, U.S. Treasury Secretary Jack Lew added his voice to a chorus of leaders from within and outside the EU about the risks of pulling out of the European Union. “I see only negative economic outcomes” if the U.K. votes to exit, Lew said in an interview to be broadcast on CNN’s “Fareed Zakaria GPS.” A Brexit would also put geopolitical stability at risk, Lew said.