A Liberal backbencher is considering seeking legal advice over allegations he told Minister Tom Koutsantonis to "speak English"

Mr Koutsantonis on Wednesday reacted angrily in Question Time to Riverland MP Tim Whetstone, believing he had told him to "speak English" in a derogatory reference to the minister's Greek heritage.

Mr Whetstone said Mr Koutsantonis had "tried to put words in my mouth" and was a "bully-boy".

"I'm very much disappointed that he would stoop into the gutter as he has," Mr Whetstone said. "I categorically deny I said 'speak English'."

The words "speak English", however, were clearly audible in a broadcast of the exchange last night. The accompanying footage on Channel 10, did not identify the source. Several Labor frontbenchers claimed they clearly heard the taunt on Wednesday.

Late yesterday, Mr Koutsantonis said he remained sure Mr Whetstone made the comment. "I think we need to move on from this - an apology - and we'll get on with governing," he said.

"It's obvious now from the tape someone said it. Let's just be man enough to admit it and move on. There's more important things for the state to deal with. It's really unbecoming just to pretend it didn't happen."

Before the audio was revealed, Mr Whetstone and Liberal frontbencher Martin Hamilton-Smith fronted a media conference to accuse Mr Koutsantonis of "fabricating" the incident. Asked if a colleague should own up to using the phrase if they said it, Mr Whetstone said: "Absolutely". "I think everyone will find that there was no slur to the minister," Mr Whetstone said.

A Liberal spokesman said the broadcast of the audio evidence did not change their position. Premier Mike Rann used Twitter to accuse Mr Whetstone of an "offensive smear".