The Guardian reports today on the witness anonymity bill, a bill that if accepted will mean all witness in criminal trials have the right to anonymity, granted by a judge, if they can show a "harm to the public interest" if their names are made public.
I can envisage only a small number of criminal trails at which anonymity for witnesses could be a good idea, for example trials for rape. It's well documented that women survivors of rape who pursue a conviction are subject to investigations into their lives and analysis of the sexual history - enough to put off anyone, but add to that the slim chance of a conviction and it's no small wonder the majority of rapes go unreported. Witness anonymity in this case could be a good thing that would spare a victim the trauma of open court cross examination.
Having said this there are some very obvious problems with witness anonymity. Never being able to know who's making claims against you and no cross examination of anonymous witnesses makes for a trail shrouded in mystery. It would be difficult, if not impossible, for a defendant to challenge the witness testimony. There are currently no safeguards proposed to prevent someone being charged based solely on secret evidence from an anonymous witness.
Call me paranoid, but in our surveillance society, where our movements are monitored (and false records could be easily created) allowing anonymous witnesses undermines the fairness of trails and gives powerful people/organisation yet another opportunity to frame an individual for a crime they did not commit.