They were ghost witnesses, a parade of men and women with fake names, electronically distorted voices and faces cloaked behind heavy curtains. No one except the prosecution knew who they were. But at the end of last month's Aston murder trial their evidence put four men in prison for a total of 135 years for the murder of Birmingham teenagers Charlene Ellis and Letisha Shakespeare.

For many lawyers, these "special measures" used to protect witnesses during the case at Leicester crown court were steps too far. Yet, the appeal court ruled them legal and the crown prosecution service supported them.