More than 50 MPs from UK PM Cameron's party ready to join EU exit campaign

By Michael Holden and William James LONDON (Reuters) - British Prime Minister David Cameron has been challenged by a group of over 50 members of parliament from his Conservative Party who are prepared to join a campaign backing Britain's exit from the European Union unless he achieves radical changes in the bloc. The MPs on Sunday launched a new political group called Conservatives for Britain (CfB), which will support Cameron's bid for reform while urging an end to EU membership unles