British Prime Minister David Cameron was forced into a hasty cabinet reshuffle on Saturday after the dramatic resignation of a senior minister that threatens to widen divisions over Europe within the ruling Conservative Party.

The rancorous departure of Work and Pensions Secretary Iain Duncan Smith, a leading campaigner for Britain to quit the European Union, also deals a blow to the political ambitions of finance minister George Osborne, commentators said.

Cameron and Osborne are both urging Britons to vote to remain in the EU in a June 23 referendum but many Conservative lawmakers and activists favor a "Brexit." The issue has riven the party for decades.