Look, Britain, if France can pass gay marriage, so can you. Prime Minister David Cameron faces a rebellion in his own party on Monday as up to 150 Conservative M.P.s threatened to vote against legalizing same-sex marriage—forcing Cameron to issue grave warnings across the aisle for support. The bill is being tabled by a former Tory minister, Tim Loughton, who opposes gay marriage, and instead has proposed an amendment that would allow for civil unions. Loughton has waged a public battle for his own amendment, claiming—without any real facts to back him up—that same-sex marriage will cost the taxpayers £4 billion in new “survivors” pensions. Labor leader Ed Milibrand could end up the real kingmaker of the bill—and he could gain some real political capital.