Steven Kay, secretary of the Criminal Bar Association, described the judge's decision to lift a ban on releasing the transcript of Keith Hall's confession as an extremely rare step.
'It (the tape) wasn't heard during court proceedings because it was not held to be admissible or reliable and he (the judge) is now putting it into the public domain,' Mr Kay said.
Michael Kalisher QC said juries regularly hear evidence from undercover police. 'There are plenty of cases where evidence is given by undercover police officers who, let's say, get involved in a drugs deal.'
But Mr Kalisher said that judges have to be particularly careful considering the admissibility of alleged confessions, especially because of several recent Court of Appeal cases in which convictions were quashed after confessions obtained by police were called into question.
Possible motives for releasing the tape might include an implied criticism of the restrictions imposed on police officers by the Police and Criminal Evidence Act, which obliges officers to caution suspects before they make a taped confession.
Helena Kennedy QC, a leading criminal lawyer, said: 'I hope that this action is not seeking to comment on some supposed flaws in the Police and Criminal Evidence Act. I personally believe it is working well and that, if judges believe to the contrary, they should restrict themselves to discussing it within the professional brotherhood.'
She said that it was important in a democratic society that the police adhere to strict rules about obtaining confessions.