An investigation into retired Liberal MP Bruce Billson has cleared him of breaching ministerial guidelines by lobbying his former parliamentary colleagues.

But the former member for Dunkley remains the subject of a separate inquiry into whether his actions constitute a contempt of parliament.

In August, Prime Minister Malcolm Turnbull asked the Department of Prime Minister and Cabinet (DPMC) to investigate whether Mr Billson had breached rules preventing former minsters from lobbying new ministers within 18 months of leaving their job.

Mr Billson is now the executive chairman of the Franchise Council of Australia, which lobbied Government MPs for changes to industrial relations legislation that passed through Parliament last month.

Mr Turnbull asked the head of the DPMC, Martin Parkinson, to investigate Mr Billson after a question from the Opposition in Parliament in August.

"Mr Billson assures me that he both understands and has complied with his post-ministerial obligations under the Standards," Dr Parkinson wrote in a letter to the Prime Minster, dated September 4.

"On the basis of the information available to me, I have no reason to conclude Mr Billson has breached either the Statement of Ministerial Standards or the Lobbying Code of Conduct."

The DPMC only made Dr Parkinson's letter public after a request from 7.30.

Mr Billson has not responded to a request for comment about the investigation.

In August, 7.30 revealed that Mr Billson failed to disclose he was receiving a $75,000 per year salary from the Franchise Council of Australia before he left parliament.

The former small businesses minister has since apologised for failing to list the salary on the official register of members' interests.

The Speaker of the House of Representatives, Tony Smith, has since referred Mr Billson to the powerful Parliamentary Privileges for an investigation into whether he should be found in contempt of parliament.

Past and present MPs found guilty of contempt face potential penalties of six months in prison and a $5,000 fine.

Loading...