A group of around 20 PwC partners are allegedly preparing to campaign the firm over a "lack of accountability" in tax leaks scandal.

Disgraced consultancy PwC is refusing to reveal the “terms of reference” — the instructions it set — for its secret internal investigation into its decade-long tax leaks affair.

An alleged mastermind of the PwC global tax leaks scam has quietly left a role overseeing a powerful Federal Government tax advisory committee run by the peak body of the Australian legal profession.

The embattled Tax Practioners Board will be forced to reveal whether its former chair — who was in charge for the entire PwC tax leaks investigation —recused himself from the probe, including from board meetings.

The long-time chair of the Tax Practitioners Board — who departed immediately before explosive senate hearings into the PwC tax scandal two weeks ago — spent almost a decade working for the same accountancy as disgraced tax practitioner Peter Collins.

An alleged mastermind of PwC’s tax leaks scheme was just weeks ago providing nationwide training seminars to the Australian Taxation Office – and was personally praised by the Taxation Ombudsman.