The Australian Communications and Media Authority investigated the interview, broadcast on August 22, in which Ms Sales grilled Mr Abbott over his claim that BHP suspended its Olympic Dam project as a result of the carbon tax.

Ms Sales extracted an admission from Mr Abbott that he had not read BHP's statement, which made no mention of the tax.

The timing could not be worse for the Opposition Leader, who is now under attack for failing to read a Federal Court judgment dismissing the sexual harassment case against the former speaker Peter Slipper.

Despite not reading the judgment, which found the case to be a politically motivated abuse of process, Mr Abbott said Mr Brough acted ''rightly at all times''.

Mr Abbott said he was too busy ''doing important things for the people of Australia'' to read the judgment.

The probe into 7.30 was sparked by two complaints (the watchdog does not name complainants). One claimed Sales's treatment of Mr Abbott ''was very bad … she made it obvious that she does not like him.''

Another stated, ''I believe [her] personal left-wing views are showing through … I also believe the ABC is responsible for a great deal of left-wing bias.''

In response, the ABC told the watchdog that Sales had employed a ''devil's advocate'' interviewing style and that it does ''not believe that posing testing questions to an interviewee and then allowing them to respond to those questions is biased or bad mannered. It is, in fact, a recognised standard of objective journalism.''

ACMA announced its investigation found no breach of the ABC's Codes of Practice.

It said: ''ACMA accepts that the nature of current affairs reporting can require presenters to be questioning, and at times sceptical, in their analysis of issues.

''Viewers of 7.30 would be familiar with [Sales's] presentation style and may expect her to conduct probing interviews, particularly when dealing with a significant and experienced politician such as Mr Abbott.''

The report said Sales ''provided several opportunities for Mr Abbott to respond to her questions and to put his views across at some length''.