Tax expert John Shewan says that claims by Andrew Little that he did not seek an apology from the Labour leader are misleading.
"The statement that I never asked for an apology is completely incorrect," Mr Shewan told the Herald today.
Mr Little told reporters this morning that he did not apologise to Mr Shewan, a former PwC chairman, over incorrect statements he made about his background in April because he was never asked to.
"I wasn't asked to provide an apology. I was asked to provide his assurance that the media report I relied on was wrong."
He added: "[Mr Shewan] explicitly said 'I don't need you to apologise, I want a correction of a statement', and that's what I've done."
When asked again to confirm that Mr Shewan had not asked for an apology, Mr Little said: "That's my recollection of the first face-to-face discussion that we had."
Following the release of the Panama Papers in April, Mr Little questioned the choice of Mr Shewan to lead an inquiry into the disclosure rules for foreign trusts based in New Zealand.
He wrongly claimed that Mr Shewan had once helped advise the Bahamas Government on how to preserve its tax haven status.
Mr Shewan said today that he originally only asked the Labour leader to retract his "defamatory" comments.
But when Mr Little failed to issue a retraction for nearly two months, he wrote back to Mr Little's office on June 10 and asked for the retraction to be expanded to include an apology.
"I specifically asked for an apology, that being because of the prolonged delay in getting the [comments corrected]," he said.
Mr Shewan said the Labour leader's office rejected this request. He was also told that any further correspondence should be sent to Mr Little's lawyer.
On the evening of June 18, a Saturday, Mr Little issued a statement retracting his comments, but stopped short of an apology.
Mr Shewan said he had been reluctant to take legal action while he was undertaking the inquiry into foreign trusts, which was publicly released yesterday.
But he was "dismayed" at Mr Little's latest comments, and would not rule out further action.
"I'm not prepared to sit by and let him say anything more defamatory.
"I would prefer not to take any legal action and I think it is unlikely that I would. But I don't just sit around and let people defame me. It's just not on."
A spokesman for Mr Little said this evening that the Labour leader had been referring to his initial face-to-face meeting with Mr Shewan, and not the subsequent correspondence between Mr Shewan and Mr Little's office.
He said Mr Shewan was satisfied with the public statement put out by Mr Little, even though it did not include an apology.
John Shewan's letter to Andrew Little's office, June 10
The suggested response is not acceptable. It does not recognise the severity of the incorrect statement made by Mr Little.
It's reasonable to expect a person in Mr Little's position to understand the impact and damage the statement he has made would have on me personally and the potential they have to negatively impact my business now and in the future.
I have been fair and extremely patient. It is close to two months since Mr Little caused me and my family considerable stress and humiliation.
My efforts to address the issue in a fair and timely way were responded to by procrastination and vain efforts to fob me off, whereas they could and should have brought a prompt resolution to this matter.
The statements made were patently wrong and damaging to my reputation and I now require an unqualified retraction which will go some way towards mitigating the damage that has already been caused.
A correction along the lines you are suggesting would be unacceptable.
I now request the statement I sent to you yesterday be issued with the following additions: 'I apologise to Mr Shewan for any embarrassment I have caused him through my statements'."
Please advise Mr Little's position by 5pm today.