The corporate whistleblower who was sacked after speaking out about the scandal inside CommInsure has told a Senate Committee he has no faith in the Commonwealth Bank's ability to investigate itself.

CommInsure's former chief medical officer Dr Benjamin Koh has told the Senate inquiry into financial advice that he was targeted for revealing allegations of unethical behaviour inside CBA's insurance arm.

The Commonwealth Bank maintains Dr Koh was dismissed for a privacy breach unrelated to his whistle blowing and that he sent 260 CommInsure documents to his personal Gmail account in breach of bank policy.

However, Dr Koh has rejected the CBA's claims and maintained he was sacked because he was a whistleblower and has since been vilified by senior CBA corporate affairs staff.

"I've got nothing to gain from doing what I did but, by implication, they have smeared me. And I've also heard that PR persons have gone around backgrounding politicians and journalists about my character," Dr Koh said.

"I don't know what they've said but it can't be anything good."

Koh fired for 'stupid, farcical reason'

Under questioning from Labor senator Sam Dastyari, Dr Koh said he had been sacked because of his revelations to a Four Corners/Fairfax investigation and not because of a privacy breach.

Dr Koh said his dismissal sent an stark warning to other whistleblowers.

"If you try to do it, you'll be in for it. I'm a medical doctor, I have my code of ethics. I'm trying to do the right thing. And I get fired for some stupid, farcical reason that I sent emails to myself," Dr Koh said.

"Every single employee at CBA will be looking at this process and saying I don't believe you. I'm going to just put my head down, pretend I didn't see anything, don't ask questions, don't question anything and get on with life."

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Dr Koh was originally scheduled to face the committee in person but gave his evidence via telephone in a bid to protect his identity.

Camera crews had been told if Dr Koh did appear in person his face was not to be filmed and he could only be shown from the back or shoulders down.

Dr Koh, who had worked at CommInsure since 2013, also said he had no faith in the internal committee investigating the allegations surrounding unethical behaviour at the insurer.

Jeff Morris, who earlier revealed the financial planning scandal at the Commonwealth Bank, told the committee he had warned Dr Koh about the risks with being a whistleblower.

"It's a classic case of deja vu all over again," Mr Morris said.

"I told Ben what it would be like and it's played out exactly as I said to him. Dr Koh went forward with this in the full knowledge that this would happen."

Follow Peter Ryan on Twitter @peter_f_ryan and on his Main Street blog.