Labour leader said he would take part after David Cameron flatly refused . Number 10 said Prime Minister would only take part in three-way debate . Broadcasters threaten to go ahead with seven leader debates regardless . Mr Miliband expected to say his rival is 'chickening out ' of debates today .
Labour leader said he would take part after David Cameron flatly refused . Number 10 said Prime Minister would only take part in seven-way debate . Broadcasters threaten to go ahead with three leader debates regardless . Mr Miliband expected to say his rival is 'chickening out ' of debates today .