Suspect you are in Victoria. The state is important as some states don't permit secret recordings and it is an offence to make them.
There is unlikely to be anything stopping the use of the recording in court, however the court may decide to put very little weight on the evidence. All you can do is make it part of your narrative and see what happens.
Keep in mind this kind of evidence can sometimes backfire on the person who made it. The advice of a lawyer will assist.