The commission, headed by retired High Court judge Dyson Heydon QC, has advised lawyers for the former prime minister and judge Bernard Murphy that they will be questioned under oath.

Other witnesses asked to provide statements and give evidence include one of Ms Gillard’s best friends, Robyn McCleod, senior solicitor John Cain junior, Queensland millionaire coal­miner and marina owner Paul Darrouzet, former AWU Victoria boss Bob Smith, and former heads of building company Thiess.

The hearings will occur over three days from September 9 when the anti-graft probe returns to its investigation of a union slush fund, which was established with legal advice from Ms Gillard to her then boyfriend, allegedly corrupt Australian Workers Union boss Bruce Wilson.

Justice Murphy headed the industrial unit at Slater & Gordon until he and Ms Gillard left the firm in 1995 amid a breakdown in trust among the firm’s partners over the discovery of the fund and a public controversy over another matter. The fund, called the AWU Workplace Reform Association, received large sums of money from Thiess in the 1990s. Shortly before she left the firm as a salaried partner, Slater & Gordon’s then boss, Peter Gordon, conducted an internal probe into the fund amid concerns that Mr Wilson, whose union was a significant client of the firm, had used it in a large fraud.

The AWU Workplace Reform Association registration documents that went to the West Australian government claimed its role was work safety and training.

During the confidential internal probe, Ms Gillard told Mr Gordon in a tape-recorded interview in 1995 that the association was really a “slush fund” for union elections. Hundreds of thousands of dollars were paid by Thiess into the slush fund.