Kemi Badenoch has branded Foreign Secretary David Lammy not serious and mocked him for his Mastermind appearance where he said Henry VII succeeded Henry VIII.
The shadow housing secretary ramped up tensions with the Labour frontbencher after he suggested climate change was a bigger threat than Vladimir Putin.
In his first major policy speech yesterday, Mr Lammy said the shifting environment was the most profound and universal source of global disorder and vowed to prioritise the issue.
But the Tories accused him of a failure of leadership at a time when the UK faces significant threats.
And Ms Badenoch, one of the favourites to take over from Rishi Sunak, was blunter about his personal attributes.
Kemi Badenoch has branded Foreign Secretary David Lammy (pictured yesterday) not serious and mocked him for his Mastermind appearance where he said Henry VII succeeded Henry VIII
He is not a serious man. He is not a serious man by any stretch of the imagination, she told Talk TV.
This goes back to his appearance on Mastermind where he said Henry VII succeeded Henry VIII.
This is who is representing us on the world stage.
What is our biggest challenge now? Its a coalition of authoritarian states that are acting and collaborating against Western interests, including the UKs interests.
Of course climate change is a challenge. But its not him having a group of people sitting in a meeting thats going to fix that. Thats what weve been doing for the last 10-15 years.
Ms Badenoch said the existing approach was only enriching China and deindustrialising the UK.
Mr Lammy, who studied law at Harvard, was a celebrity guest on the BBCs Mastermind show in 2008.
However, he had a torrid time, including confusing Marie Antoinette with Marie Curie. When asked who succeeded King Henry VIII, he replied: Henry VII.
Mr Lammy opened his address at Kew Gardens, south-west London yesterday, by saying: Conflicts in Ukraine and the Middle East have dominated my time in office so far. But I was very clear in opposition that, in this job, I would focus on the most profound and universal source of global disorder – the climate and nature emergency.
Justifying his decision to concentrate on the issue, he said: The threat may not feel as urgent as a terrorist or an imperialist autocrat, but it is more fundamental. It is pervasive and accelerating towards us at pace.
Yet Downing Street declined to endorse Mr Lammys claim that climate change is the biggest threat to the UK.
Asked whether the PM agreed, a No 10 spokesman said: He thinks that climate change is a huge challenge which faces us all. That is why as part of the UKs reset on the world stage, he believes it is important for the Government to position itself as a leader on climate change.
Ms Badenoch told Talk TV that Mr Lammy was not a serious man by any stretch of the imagination
Mr Lammy, who studied law at Harvard, was a celebrity guest on the BBCs Mastermind show in 2008
Mr Lammy announced a Global Clean Power Alliance of countries to focus on green energy and said he would appoint a UK special representative for climate change and nature.
He said a hard-headed realist approach using diplomatic and financial levers was needed to slow rising temperatures.
Condemning the previous Conservative government as climate dinosaurs, he said they had relied too much on fossil fuels rather than renewables.
Mr Lammy said: Im committing to you that, while I am Foreign Secretary, action on the climate and nature crisis will be central to all the Foreign Office does.
Since taking power Labour has brought forward the ban on sales of new petrol and diesel cars and the phasing out of oil and gas drilling in the North Sea.
It has also paved the way for more wind turbines, solar panels and electricity pylons to be built.