A cabinet minister's office in the Abbott government is believed to be at the heart of a dirty tricks campaign which has rocked the Napthine government, with an official investigation closing in on senior advisers.
It is understood an internal investigation is looking "very closely" at senior staff from a federal member's office.
It follows the theft of a recording device from Sunday Age reporter Farrah Tomazin which contained a private conversation with Ted Baillieu during which the former premier is critical of some colleagues.
The conversation was distributed to party members in an email purporting to be from a Liberal Party member (who does not exist). As revealed by The Age on Twitter on Thursday evening, a detailed examination of membership records has lead party officials to hone in on staff working in a federal cabinet minister's office.
It can also be revealed that senior federal advisers were on Thursday calling MPs attempting to hamper investigations.
The revelations have already created another damaging distraction for the Napthine government, which is trailing Labor 41 per cent to 59 per cent according to the latest Age/Nielsen poll.
They now have the potential to cause a significant headache for the Abbott government and one of its senior ministers.
It is understood that although there is no hard evidence, there are suspicions that staff in the federal minister's office have either been directly involved in the release of the private conversation or have knowledge relating to who was responsible.
If correct the revelations confirm a taxpayer funded dirty tricks campaign aimed at destabilising the state government and undermining rivals in the Liberal Party.
One of the advisers did not return calls from The Age, although the individual is understood to deny the claims. There are no suggestions that the federal minister was aware that Liberal membership lists had been inappropriately accessed or that a private conversation had been emailed or inappropriately obtained.
Liberal Party state director Damien Mantach has barred offices for the federal seats of Kooyong, Menzies, Goldstein, Higgins and Melbourne Ports from accessing an online database containing Liberal membership details while the investigation is under way. It is understood it will be concluded in about a week.