Hi Diane,
Which court was it in?
What kind of matter was it and has it been decided?
Was the outcome of the matter influenced by the witness' testimony? If so, then this may be a valid reason to either throw out the charges or have a re-trial.
When, where and to whom did the witness admit that they committed perjury?
Have the police been made aware of the perjury? The police can prosecute the witness and the penalties for perjury in NSW can range from a fine or suspended sentence to the maximum penalty of 10 years imprisonment (section 327 of the
Crimes Act 1900 (NSW)). See the
NSW Police Handbook which sets out what is required for the police to prosecute an offence of perjury (essentially: unless by admission, it can be hard to prove.)