Bangladesh is planning to introduce voluntary sterilisation in its overcrowded Rohingya camps, where nearly a million refugees are fighting for space, after efforts to encourage birth control failed.More than 600,000 Rohingya have arrived in Bangladesh since a military crackdown in neighbouring Myanmar in August triggered an exodus, straining resources in the impoverished country.The latest arrivals have joined hundreds of thousands of Rohingya refugees who fled in earlier waves from Myanmar&