The probe follows revelations that the firm’s former tax partner Peter Collins shared confidential information within the firm regarding multinational tax measures it was helping Treasury to develop in 2015.

The accounting firm subsequently used the confidential information to advise major corporations on how to sidestep the tax changes and market the firm.

PwC’s newly appointed chief executive Kevin Burrowes appeared alongside senior executives Jan McCahey and Catherine Walsh in Canberra on Thursday.

In his opening statement to the committee, Mr Burrowes reiterated the firm’s remorse following the scandal that has beset the firm.

“For this, I am sorry … and PwC Australia is sorry to our people, our clients, our stakeholders,” he said.

“To the government and to the Australian people, we cannot apologise strongly enough for breaching the trust placed in us and we accept the justifiable questions this matter raised about our trustworthiness and integrity.”

PwC has lost its “social licence”: Pocock

Greens senator Barbara Pocock criticised the firm over its insufficient response, arguing that the Senate and the Australia public “no longer trust” PwC to implement new “self regulation” measures.

“You‘ve got self regulatory actions that you’re voluntarily committed … They’re motherhood statements about how good governance should look,” Senator Pocock said.

She said there were no regulatory consequences if the firm didn’t abide by the recent changes it had adopted to improve governance and accountability.

“They do not have teeth, and they do not constitute a significant shift,” she said.

“You have lost the social licence to self-regulate and the self-regulations you offer are completely inadequate to the challenges and the disaster that you presented to the Australian people.”

But Mr Burrowes said the firm had adopted almost two dozen recommendations in the Switovski review and was not in a position to change government regulations.

“I’m not in a position to be able to regulate my firm,” he said.

PwC’s processes ‘crap’

Committee chair Liberal senator Richard Colbeck questioned how the business could possibly regain the trust and respect of government clients again.

“On what basis can you say to us today that any of this is going to change?” Mr Colbeck asked.

Senator Colbeck said the firm already had significant processes in place to prevent wrongdoing at the time that had demonstrably failed.

“How outrageous we see this is and … I genuinely wonder how you believe that you can recover trust when all of the systems that you say that you have, all of the procedures that you say that you have, at a local and a global level were ignored,” he said.

The Switovski report showed how “crap things were inside (the) business,” Senator Colbeck said.

PwC’s ‘shadow’ culture previously revealed

In September, PwC was savaged in an independent review run by former Telstra boss Ziggy Switkowski that exposed the firm’s “shadow culture”.

The review consistently found the attitude among staff that “revenue is king” and partners who exceeded their KPIs were treated as “heroes”.

The report painted a brutal and unaccountable culture atop the big four firm, which was driven by a “growth at all costs” mantra with a myopic focus on “revenue, revenue, revenue”.

In an attempt to rebuild trust with the government, PwC hived off its government consulting arm and sold it to private equity firm Allegro Funds for $1 in July

Former chief executive Luke Sayers, who has since departed the business, is set to appear later on Thursday morning.

More to come