But Chris Enright from the Roc rejected claims he started probe to help the senator discredit Shorten

The union watchdog official who launched an investigation into the AWU “assumed” Michaelia Cash had a political agenda when she sent him two “referral” letters about the alleged misuse of union funds, a court has heard.

But Chris Enright, the executive director of the Registered Organisations Commission (the Roc), rejected claims he started the probe to help Cash discredit the Labor leader, Bill Shorten, who was the union’s boss when it donated to the activist group GetUp.

The AWU is challenging the legality of the investigation, which led to dramatic police raids on the union’s offices on 24 October 2017, saying Enright’s decision was influenced by what it claims were Cash’s “political purposes”. The Roc was seeking to determine whether the money had been spent in line with union rules.

Under cross-examination from the AWU’s lawyer, Herman Borenstein, Enright told the court on Thursday that Cash was on a “political side of parliament” that would “clearly” have had an agenda.

“What was in her mind exactly I don’t know … I assumed she had an agenda, if I can put it that way,” Enright said.

But he said people who made referrals to regulators “invariably … have some preferred outcome or have their own agenda”.

At least some MPs see themselves as partisans with knuckledusters | Katharine Murphy Read more

“It’s incumbent upon skilled investigators to be alive to that,” he said.

He also said he knew the decision to investigation the allegations would be damaging to Shorten if made public.

Asked he if had acted to support Cash’s “political purpose”, Enright replied: “I entirely reject that proposition.”

Claiming the investigation was politically motivated, the union cited the letters from Cash and claimed that her staff leaked news of the raids to the media after a tipoff from a Roc media adviser. The adviser, Mark Lee, denied those claims in court last week.

Enright disputed letters sent from Cash to Roc represented a “referral”.

“Referral has a particular legal meaning,” he said.

Shown various correspondence written by the Roc and by Enright himself that subsequently described the letters as a “referral”, the Roc official said he been using the term “loosely”.

He also defended his decision to deal directly with the minister’s offices on a number of occasions.

“We guard our independence jealously,” he said of the Roc, which is independent of the government.

This month, Cash denied in court writing to the Roc in a bid to damage Shorten, saying she was concerned about the potential misuse of union funds.

Senate Estimates heard last week that the taxpayer-funded legal bills for Cash and the Roc have already topped $800,000.

The trial continues.