Police have questioned an ex-News of the World reporter over claims that Andy Coulson asked him to hack into phones.
Sean Hoare's solicitor, David Sonn, said he was interviewed by Met Police officers under caution but was not arrested.
The phone hacking row erupted again earlier this month after Mr Hoare made the claims about Mr Coulson - the former News of the World editor who is now the Tories' communications chief - in an article in the New York Times.
Mr Coulson denies any knowledge of the practice which resulted in his former royal editor Clive Goodman and private investigator Glenn Mulcaire being jailed for accessing the voicemails of public figures.
A Westminster sleaze watchdog has announced it will consult parliamentary and legal experts on whether hacking MPs phones is a "contempt of parliament".
MPs voted last week to refer allegations that politicians' mobiles were targeted by newspapers to the standards and privileges committee. After a preliminary meeting, the cross-party body of MPs said it would not consider any specific allegations until it had looked into the wider issues.
