U.K.'s David Cameron and Boris Johnson Clash As Brexit Battle Lines Drawn

Britain's Prime Minister David Cameron, right, and London Mayor Boris Johnson, April 22, 2015. The old friends are now on opposing sides of the debate over the U.K.'s upcoming EU membership referendum. Toby Melville/Reuters

Britain's Prime Minister David Cameron clashed with his former ally Boris Johnson in heated exchanges in parliament on Monday over the U.K.'s upcoming EU membership referendum.

Johnson, a Conservative MP and mayor of London, announced on Sunday that he would campaign against Cameron for Britain to leave the European Union, despite public overtures from the prime minister aimed at coaxing Johnson to his side.

Speaking in Parliament today, Johnson asked Cameron: "To explain…in exactly what way this deal [on Britain's terms of EU membership] returns sovereignty over any field of lawmaking to these Houses of Parliament."

Cameron responded: "This deal brings back some welfare powers, it brings back some immigration powers, it brings back some bailout powers, but more than that, because it carves us forever out of 'ever closer union,' it means that the ratchet of the European court taking power away from this country cannot happen in future."

The exchange followed remarks by Cameron that were widely interpreted as a coded attack on Johnson.

During a statement on the prime minister's renegotiation of Britain's terms of membership, completed on Friday, Cameron dismissed suggestions made by many Euroskeptics—and implied on Monday by Johnson in his weekly column in The Daily Telegraph that he used to outline his stance—that Britain could use a Leave vote in the referendum as a bargaining chip for a better deal with Brussels.

"I won't dwell on the irony that some people who want to vote to leave apparently want to use a Leave vote to remain," Cameron said. "Such an approach also ignores more profound points about democracy, diplomacy and legality.

"I have known a number of couples who have begun divorce proceedings," he added. "But I do not know any who have begun divorce proceedings in order to renew their marriage vows.

"Having a second renegotiation followed by a second referendum is not on the ballot paper."