London Mayor Boris Johnson, a heavyweight conservative, has announced that he will back the call for Britain to leave the European Union in a national referendum on the country’s EU membership.

The yesterday’s announcement was regarded by the British media as a blow to Prime Minister David Cameron’s efforts to keep Britain in the EU as Johnson was an eloquent Speaker and popular among voters. Mr Cameron announced on Saturday that Britain would hold a referendum on June 23rd to decide whether to stay or leave the European Union and recommended British people to choose remaining inside the EU, following a deal with leaders of other EU countries which gives UK a special status in the community.

Mr Cameron is scheduled to speak in the British Parliament today to kick off the campaigns before the referendum. Opinion polls have shown that the British public is almost evenly divided while many ruling Tory politicians, including six cabinet members, will side with the so-called Brexit camp.