The issue focused on by the families of those who died in the Hillsborough disaster has been raised by the Police Federation.In a letter to the prime minister, it says that by 2011-12 the force had received only 10 complaints about police officers who had made errors of judgement.It says that this has led to an under-investment in training and changes to its policies.The federation also points out that "no specific policies have been issued to prevent officers from making mistakes of judgement".In his letter, Mr