The purpose of s 128 of the Evidence Act may be gleaned from the tenor of the words used within it. Throughout, references are to the giving of future evidence, to which a certificate shall attach: "to giving particular evidence" in s 128(1); "the court is not to require the witness to give that particular evidence" in s 128(2); "If the witness gives the evidence" in s 128(3); "The court is also to cause a witness to be given a certificate under this section if: (a) the objection has been overruled; and (b) after the evidence has been given, the court finds that there were reasonable grounds for the objection" in s 128(4); "... the court may require the witness to give the evidence" in s 128(5). Section 128 does not contemplate that a certificate might issue in respect of evidence already given save where the evidence is given over an objection by the witness to giving evidence.
184 The terms of s 128 clearly contemplate that a certificate, if granted, is granted prior to the giving of evidence not to evidence which has already been given, particularly where no objection was taken.
185 To the extent that a certificate can be issued after the giving of evidence, this may occur where the court has ruled but not granted a certificate: Cornwell v R [2006] NSWCCA 116 at [87] - [94]. The certificate in that proceeding concerned answers concerning specific matters, in cross-examination.
186 A retroactive application of s 128 is unwieldy and is not contemplated by that section. It also undermines the purpose of the section, which is to prevent witnesses from being coerced into giving evidence which tends to incriminate them. Once the evidence has been given, it cannot be said that the witness has been compelled.