A climate protester was left speechless after a radio talk show host suggested concrete can be grown on trees.
Mr Ford was asked what he did for a living, telling the broadcaster he was a carpenter.
Mr Graham then asked how safe carpentry is for the environment and whether it was is compatible with reaching climate goals.
Mr Ford explained that he worked with timber, which is more sustainable than building with concrete.
"But you work with trees that have been cut down... how is it sustainable if you're killing trees?" Mr Graham asked.
"Because it's regenerative, you can grow trees," Mr Ford replied.
Mr Grahmam responded by saying that "you can grow all sorts of things, can't you?".
"Well you can't grow concrete," Mr Ford hits back before Mr Graham says: "Yeah you can".
One of the main components of concrete is limestone. Making concrete is a carbon-intensive process that usually requires the burning of fossil fuels.
A period of silence then ensues and Cameron remains on air. Mr Graham then terminates the interview. "See you Cameron, cheerio," he says.
"That was Cameron. He grows trees, then cuts them down, then makes things from them. Brilliant. Marvellous."
Insulate Britain has carried out more than 10 protests in recent weeks by blocking roads mainly in southern England, causing traffic disruption.
On Tuesday the group ramped up its campaign ahead of the Cop26 summit in Glasgow, warning motorists to avoid the M25 after declaring the motorway “a site of nonviolent civil resistance”.
It has called for drivers to either not use the major road from 7am on Wednesday or to reduce their speed to 20mph “to minimise the risk of accidents”.
In a statement, the group said: “In light of a national injunction covering England’s highways, Insulate Britain has declared the M25 a site of nonviolent civil resistance and called for motorway traffic to be slowed.
“Starting from 7.00 on the morning of Wednesday 27 October the M25 will become a place of nonviolent civil resistance to stop our government committing crimes against humanity.
“We ask that: People do not use the M25, or if they do, speeds are reduced to 20mph to minimise the risk of accidents.”
Insulate Britain, an offshoot of Extinction Rebellion, wants the government to insulate all UK homes by 2030 to cut carbon emissions.
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