David Cameron was forced to face his fellow European leaders Tuesday after his humiliating defeat in Britain’s referendum on membership in the European Union. Cameron was due to meet Jean-Claude Juncker, the European Commission president, to discuss ways to proceed after Britain’s vote to leave. Speaking before the meeting, Juncker slapped down British suggestions that negotiations could begin before London formally triggers its exit from the EU. “They have expressed their view. Now there have to be consequences,” he said. “There can be no secret negotiations. No. No secret negotiations.” Britain had hoped to begin talks without the two-year countdown that would be activated once the British prime minister invokes Article 50.