Geoffrey Watson reacted angrily after facing scrutiny at Queensland's Commission of Inquiry into the CFMEU when it emerged he had not recorded conversations with witnesses and instead relied on handwritten notes.
The barrister - whose damning report of the union sparked the state's CFMEU probe - was recalled to the inquiry for cross-examination on Thursday by counsel for former union bosses Jade Ingham and Michael Ravbar.
He became agitated under sustained questioning by Ruth O'Gorman, acting for Mr Ravbar, who queried the methodology and reliability of Mr Watson's report.
After an adjournment, commissioner Stuart Wood intervened to remind Mr Watson to concentrate on answering Ms O'Gorman's questions, suggesting his answers were becoming argumentative and non-responsive.
"It's up to you how you wish to handle this witness," he told Ms O'Gorman.
Mr Watson insisted witnesses would not be fully frank with him if they were being recorded.
"When I say that people don't talk, they clam up," he said.
In a testy exchange, Ms O'Gorman asked whether the absence of complete records of the interviews he conducted made it impossible for anyone other than himself to assess the value of his conclusions.
"I do not accept the premise of your question," Mr Watson replied.
"The premise of your question is that there was an absence of detail in my notes which would prevent a person from making such an assessment. I don't accept that premise."
Ms O'Gorman then asked whether the commission would find his handwritten notes a sufficiently accurate account of all the information he received, prompting a fiery response.
"I'm sorry, are you asking me to speculate on what the commissioner might find?" Mr Watson said.
"I might remind you this is not a commission into me or my report. I'm not going to speculate on that."
Ms O'Gorman is expected to continue her cross-examination of Mr Watson next week.
Earlier, an ex-minister denied claims she threatened to tear up a developer's contract for the $1.6 billion Toowoomba bypass project in 2018 if he did not co-operate with the CFMEU.
Grace Grace, the former Labor government's industrial relations minister, had come under fire from the Liberal National administration after the allegation was made at the CFMEU probe.
"I deny the allegations," Ms Grace told reporters on Thursday.
"I will let the commission continue with its processes and all the evidence from this issue will come out at the appropriate time.
"As the matter is before the commission, that's all I can really say. I have not yet been called, but if so, I will then put my side."
Jose Sanchez - a former Acciona project director for the Toowoomba Second Range Crossing - made the allegation at the inquiry, saying Ms Grace was "aggressive".
Asked if Mr Sanchez was lying, Ms Grace said: "I am saying I deny the allegations."
Deputy Premier Jarrod Bleijie told reporters Ms Grace should resign as Labor's industrial relations spokesperson.
"She should not be in that position," he said.
"These are serious allegations. She was a senior minister."
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