A private investigator who intercepted mobile phone messages while working for a tabloid newspaper has launched the latest round of a court battle to protect his "legitimate legal interests".
Glenn Mulcaire, who worked for the News of the World, asked the Supreme Court to rule on whether he must disclose who instructed him and to whom he passed the information.
Mr Mulcaire was in court for the first day of the hearing in London on Tuesday, which is expected to end later this week, the Press Association reported.
Five Supreme Court justices are being asked to decide whether "intercepted confidential information" is intellectual property and what detail Mr Mulcaire must reveal.
Mr Mulcaire appealed to the Supreme Court - the UK's highest court - after losing fights in the High Court and Court of Appeal.
Five years ago Mr Mulcaire and former News of the World royal editor Clive Goodman were jailed after the Old Bailey heard how they plotted to hack into royal aides' telephone messages.
More police inquiries into phone hacking by journalists have started since then and scores of celebrities have launched civil damages claims in the High Court.
Mr Mulcaire had again been arrested, in December, following the launch of the new police investigation, the Supreme Court heard.
A lawyer told judges that Mr Mulcaire had been released on bail without charge pending further inquiries.
Mr Mulcaire said, in a statement released before the start of today's hearing, that he had been advised by lawyers that he should "not have to give potentially incriminating answers" to questions asked in civil litigation.
"This appeal is being heard because I have been advised by my legal team from the outset that I should not have to give potentially incriminating answers to questions asked of me in phone hacking cases in the High Court," he said. "I bring it for no other reason."
He added: "The police have all the relevant documents from me since 2006 and I have already faced criminal proceedings, been convicted, and served a prison sentence.
"All the steps taken by my legal team in respect of the civil claims against me are to protect my legitimate legal interests."
Gavin Millar QC, for Mr Mulcaire, outlined the case to judges at the start of today's hearing.
He said Mr Mulcaire wanted the Supreme Court - the highest in the UK - to decide when he could "properly claim privilege against self-incrimination".
"Mr Mulcaire brings this appeal because he believes he is entitled under certain circumstances to assert privilege against self-incrimination," said Mr Millar.
"He does so because of the risk he may be charged with ... criminal offences."
Mr Millar added: "He will, of course, accept the ruling of this court as the final court of appeal."
He said Mr Mulcaire was in the unusual situation of having to "predict what he may be charged with".
Mr Mulcaire began his Supreme Court fight after Nicola Phillips, who was an assistant to public relations consultant Max Clifford, claimed that her voicemail had been unlawfully intercepted.
Judges in the High Court and appeal court ruled that Mr Mulcaire should disclose information relating to Ms Phillips' claim. Mr Mulcaire then appealed to the Supreme Court.
Five Supreme Court justices - Lord Hope, Lord Walker, Lord Kerr, Lord Clarke and Lord Dyson - are expected to hear evidence over three days.
The hearing continues on Wednesday.