In the letter, Mr Smith, who is a vocal supporter of the need to act on climate change, said that it was in News's commercial interests to oppose the idea that people were responsible for the rise in global temperatures.

"And I'm on to you. When friends ask me why your organisation runs such opposing views on climate change – from Fox News's claims that it's all bunkum to The Australian newspaper occasionally claiming it's accepted science - I am able to say: 'It's simple,'" he writes.

"It's all about making more money. They have worked out they will get more advertising and make more money on Fox News if climate change is debunked using sensationalism while they are likely to get greater circulation and more advertising dollars if The Australian shows a different view, so staff are directed accordingly."

In the letter Mr Smith also claims Mr Williams was personally getting involved in rejecting one of Mr Smith's ads because it mentioned the Murdoch press. In April Mr Smith said that he tried to book an ad in Sydney's Daily Telegraph to promote his Wilberforce Awards - which reward young people with leadership qualities. The ad also offered a $5000 reward to any journalist who could get the issue of climate change and finite resources covered in one of Mr Williams's papers.

Mr Smith said he found most journalists at News to be professional and fair-minded but that they censored themselves to please their boss.