Competition regulator Graeme Samuel has moved to clear the air over a bitter controversy surrounding attempts to lay criminal charges against the late billionaire and Visy boss, Richard Pratt.

Speaking on video on Wednesday with Alan Kohler, Robert Gottliebsen and Stephen Bartholomeusz, Mr Samuel highlighted the crucial role played by the Director of Public Prosecutions (DPP) in the legal process which led to criminal charges being laid against the packaging king.

He also asked the public to value the separation of roles between the Australian Competition and Consumer Commission (ACCC), which investigated the Pratt case, and Chris Craigie, the Commonwealth DPP.

“I think it’s a very interesting and a very useful discipline to have that division of roles – the investigator on the one hand and the prosecutor on the other hand,” Mr Samuel said.

Mr Samuel strenuously defended all aspects of the case, which began with a successful civil prosecution against Mr Pratt, and ended with ultimately unsuccessful attempts to bring criminal charges against the ailing tycoon, who died within hours of hearing a criminal case against him had effectively been quashed.

Asked if the experience of Mr Pratt and Visy before the ACCC — where a civil case was later followed by a criminal case — would create reservations in the business community about volunteering information to the regulator, Mr Samuel said: “The legal community understands what is required … if they are going to undertake a civil settlement with us.”

In a wide-ranging interview, Mr Samuel revealed the full circumstances surrounding Commonwealth Bank of Australia’s dramatic takeover of regional lender BankWest in the depths of last year’s global financial crisis, describing the immediate context of the takeover as ‘unusual’ and implying that if CBA had not bought the regional bank, it may not have been saved from becoming a ‘non-existent force’.

Mr Samuel did not go as far as saying BankWest was under threat of going broke, but suggested that advice from key stakeholders, including the RBA, was that the WA-based bank, then owned by troubled UK bank HBOS, was at risk of “severely contracting”.

The competition chief also offered his own review of former Telstra Corp Ltd chief Sol Trujillo’s contentious reign at the telco, recalling the regulator’s court wins during the Trujillo reign and confirming the ACCC’s position that there should be structural separation at the telecommunications company because light-handed ‘operations separation’ had been a failure.