Owen Paterson, who was sacked as Environment Secretary in this week’s Cabinet reshuffle, is preparing to speak publicly of his doubts that climate change is man-made.

Mr Paterson, who was replaced by Liz Truss, is to deliver the annual lecture to the Global Warming Policy Foundation (GWPF), the climate-sceptic organisation set up by the former Chancellor Lord Lawson.

His decision is a foretaste of the trouble Mr Paterson, who is firmly on the Right of the Tory party and a staunch Eurosceptic, could cause for David Cameron.

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The Prime Minister has warned that climate change is among the most serious threats facing the world and pledged to lead Britain’s greenest ever government.

However, spending on climate change work was slashed during Mr Paterson’s time running the Environment Department and he even argued global warming could be good for the country.

He has now made the clearest declaration of his climate change scepticism by agreeing to deliver the keynote speech to the foundation in October.

Lord Lawson has said his think-tank is “open-minded on the contested science of global warming”, but “deeply concerned about the costs and other implications of many of the policies currently being advocated”.

Critics have labelled its supporters “climate change deniers” and accused them of using unscientific material to bolster their claims.

Shape Created with Sketch. Government reshuffle Show all 10 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. Government reshuffle 1/10 William Hague Standing down as: Foreign Secretary, though Hague stays in the Cabinet as Leader of the House Getty 2/10 Kenneth Clarke Out: The Minister Without Portfolio resigns after a marathon 22-year stint Getty 3/10 Andrew Robathan Out: As Northern Ireland Minister. Prior to that he was Minister of State for the Armed Forces AP 4/10 Alan Duncan Out: As International Development Minister. He has been the Conservative MP for Rutland and Melton since 1992 Rex 5/10 Greg Barker Out: As Energy and Climate Change Minister. He has served as MP for Bexhill and Battle since 2001 Rex 6/10 Nick Hurd Out: As Minister for Civic Society. He has been the Conservative MP for Ruislip, Northwood and Pinner since May 2010 Rex 7/10 Damian Green Out: As Policing Minister. MP for Ashford since 1997 Getty 8/10 Dominic Grieve Out: As Attorney General. Previously held a number of positions in the shadow cabinet including Shadow Attorney General and Shadow Secretary of State for Justice Getty 9/10 David Willetts Out: As Universities Minister. Began his career in Parliament as the MP for Havant in 1992 Getty 10/10 David Jones Out: As Welsh Secretary. Held the position of Shadow Minister for Wales from 2006 to 2010 Getty 1/10 William Hague Standing down as: Foreign Secretary, though Hague stays in the Cabinet as Leader of the House Getty 2/10 Kenneth Clarke Out: The Minister Without Portfolio resigns after a marathon 22-year stint Getty 3/10 Andrew Robathan Out: As Northern Ireland Minister. Prior to that he was Minister of State for the Armed Forces AP 4/10 Alan Duncan Out: As International Development Minister. He has been the Conservative MP for Rutland and Melton since 1992 Rex 5/10 Greg Barker Out: As Energy and Climate Change Minister. He has served as MP for Bexhill and Battle since 2001 Rex 6/10 Nick Hurd Out: As Minister for Civic Society. He has been the Conservative MP for Ruislip, Northwood and Pinner since May 2010 Rex 7/10 Damian Green Out: As Policing Minister. MP for Ashford since 1997 Getty 8/10 Dominic Grieve Out: As Attorney General. Previously held a number of positions in the shadow cabinet including Shadow Attorney General and Shadow Secretary of State for Justice Getty 9/10 David Willetts Out: As Universities Minister. Began his career in Parliament as the MP for Havant in 1992 Getty 10/10 David Jones Out: As Welsh Secretary. Held the position of Shadow Minister for Wales from 2006 to 2010 Getty

Last year’s guest speaker was the former Australian Prime Minister, John Howard, who described climate change campaigners as “zealots” and “alarmists” who pursued “a substitute religion”.

Last week the foundation suffered the embarrassment of being ordered by the Charity Commission to split into separate educational and political arms.

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The commission explained that some of its activities “breached what is expected of an educational charity, namely that the material lacked balance and promoted a particular line of opinion”.

Guy Shrubsole, a climate change campaigner with Friends of the Earth, said: “This is beyond satire, and confirms Owen Paterson was never fit to hold the post of Environment Secretary.

“Liz Truss must make a clean break with her predecessor by backing urgent action to slash emissions, and by speaking to scientists and experts – not the climate quacks at the GWPF.”

A spokesman for Greenpeace, Ben Stewart, said: “Some people would say that for the last two years Paterson has been delivering a rolling 24/7 lecture for the GWPF. Maybe it’s for the best he’s come out of the closet and formalised the relationship.”

Mr Paterson’s dismissal caused dismay among Right-wing allies who had lobbied hard against the move. Some Cameron loyalists believe the Prime Minister could have stored up trouble by returning him to the backbenches, where he could become a focus of dissent.

He made no secret of his dismay over being fired and signalled he was preparing to set out his views in public. He told Mr Cameron in his departure letter: “At this critical moment in our nation’s history, I have clear ideas on the future of the UK and its place in the world.”

During this week’s Prime Minister’s Questions, Mr Paterson was deep in conversation with the former Cabinet minister Liam Fox, who turned down an offer of a junior post from Mr Cameron. Their appearance together prompted speculation they could lead internal opposition to Mr Cameron.

Downing Street is relying on Mr Paterson deciding not to rock the boat ahead of the general election to avoid charges he is highlighting the party’s internal divisions.