The Prime Minister’s plans for gay marriage could leave churches facing legal action unless they agree to same-sex unions, it emerged today.Legal advice reportedly sent to David Cameron warns that church could be sued under human rights legislation if they refuse to allow the services to proceed. Exemption granted to the Church of England by the Coalition Bill to prevent it having to conduct gay marriages is “eminently challenge-able” in the European Court of Human Rights. It also warns that the Government's insistence that protections put in place for other religious groups who don't want to marry homosexuals could be...