ICAO Chicago convention, Annex 13 states in paragragraph 5.12 Non-disclosure of records that the following records should not be made available for any purpose other than accident prevention:
a) All statements taken from persons by the investigation authorities in the course of their investigation.
b) All communications between persons having been involved in the operation of the aircraft
c) Medical or private information regarding persons involvedin the accident or incident
d) Cockpit voice recordings and transcripts of such recordings
e) Opinions expressed in the analysis of information including flight recorder information.
The above basically means that the legal investigation will have to interview its own witnesses, the legal investigation cannot use the Cockpit Voice recording, and the legal investigation cannot use the parts of the safety investigation that do not constitute factual information.
The legal investigation can use the data from the flight data recorder, and all factual information gathered in the course of the safety investigation other than that mentioned above.
In view of the need to prevent situations of self-incrimination it seems logical that witness statements given to the safety investigators and cockpit voice recordings are not available for the legal proceedings.
Whether an individual state has filed an exemption to annex 13 varies, but in many cases the convention has been ratified in legislation, and the CVR is not available for legal proceedings.
legalapproach:
CVR's
On basic principles a CVR recording would be admissible in evidence in a UK court. It is real evidence.
It may be real evidence, but it is self incriminating, and if it will be used to prosecute pilots, then may pilots will turn it off.