Finance Minister Mathias Cormann has declared he has never been in favour of an iron ore inquiry, despite saying earlier this week that an investigation could be a sensible idea.

Fortescue Metals Group chairman Andrew “Twiggy” Forrest has been pushing for an inquiry into the market, arguing big mining companies are deliberately driving down the iron ore price.

It is a claim strongly rejected by Rio Tinto and BHP Billiton.

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Independent Senator Nick Xenophon has also been lobbying the Government to endorse a parliamentary investigation.

The Finance Minister on Monday said the inquiry could be a “sensible” idea.

But on Wednesday Mr Cormann voiced his opposition to the probe in an interview on Sky News.

“I’ve never been in favour of an inquiry into the iron ore sector,” he said.

Mr Cormann said he always took the view that an inquiry needed to be “sensible”, but he has questioned if it is needed at all.

“I don’t think there’s much that we don’t know,” he said.

“I mean we know that there is a market that is operating freely.”

Trade Minister Andrew Robb and Industry Minister Ian Macfarlane have also argued an inquiry is unnecessary.

Prime Minister Tony Abbott on Friday indicated he was in favour of it, telling Macquarie Radio: “I think we do need an inquiry”.

But this week he has distanced himself from those comments and warned of a “one-sided” investigation that could “degenerate into a witch-hunt” against the big miners.

Mr Forrest said big mining companies are trying to avoid transparency by lobbying against a parliamentary investigation.

“I’ve noticed even from Perth the amount of energy, the amount excitement which the multi-nationals have put into a major lobbying campaign in Canberra and everywhere all through the papers to try and avoid an inquiry,” he told ABC’s 7.30 program on Tuesday night.

“I’ve never seen two quite conservative companies work so hard against the cause of transparency.”

– ABC