Boris Johnson has issued a slapdown to Emmanuel Macron over the French president's threat to veto a EU trade deal with South American states including Brazil, claiming that concern over the Amazon fires was being used as an "excuse" to interfere with free trade.

Mr Macron has warned that he will block the EU-Mercosur deal - on the brink of completion after 20 years of talks - unless Brazil's far-right president Jair Bolsonaro shows he is taking seriously his duty to protect his country's environment as part of the global fight against climate change.

Arriving at the G7 summit hosted by Mr Macron in the French coastal resort town of Biarritz, Mr Johnson restated his horror at the thousands of wildfires currently wreaking devastation across swathes of the Brazilian Amazon.

Amazon rainforest swept by fires: In pictures Show all 25 1 /25 Amazon rainforest swept by fires: In pictures Amazon rainforest swept by fires: In pictures Fire rages in the Amazon rainforest in the Brazilian state of Rondonina on August 23 Reuters Amazon rainforest swept by fires: In pictures Smoke billlows from burning tracts of the Amazon rainforest in the Brazilian state of Para on August 23 AFP/Getty Amazon rainforest swept by fires: In pictures Fire rages in the Amazon rainforest in the Brazilian state of Rondonina on August 23 EPA Amazon rainforest swept by fires: In pictures Land in the Amazon rainforest left scorched in the fires in the Brazilian state of Rondonina on August 23 AFP/Getty Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil on August 23 AFP Amazon rainforest swept by fires: In pictures Fire tears through a farm in the Brazilian state of Mato Grosso AP Amazon rainforest swept by fires: In pictures An area of the Amazon rainforest left scorched in the fires in the Brazilian state of Amazonas on August 24 AFP/Getty Amazon rainforest swept by fires: In pictures Satellite images show a series of fires in the southwest Brazilian state of Rondonia on August 15 AP Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil Reuters Amazon rainforest swept by fires: In pictures A satellite image released by NASA shows the active fires that have been detected in the Amazon region EPA Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Amazonas, Brazil Reuters Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil Reuters Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Rondonia, Brazil Reuters Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Amazonas, Brazil Reuters Amazon rainforest swept by fires: In pictures Indigenous people from the Mura tribe wallk in a deforested area inside the Amazon rainforest in the Brazilian state of Amazonas on August 20 Reuters Amazon rainforest swept by fires: In pictures Fire tears through a farm in the Brazilian state of Mato Grosso AP Amazon rainforest swept by fires: In pictures Smoke billows from a stretch of fire in the Amazon rainforest in the Brazilian state of Rondonia on 23 August AFP/Getty Amazon rainforest swept by fires: In pictures Smoke billows during a fire in an area of the Amazon rainforest in the state of Amazonas, Brazil Reuters Amazon rainforest swept by fires: In pictures Indigenous people from the Mura tribe wallk in a deforested area inside the Amazon rainforest in the Brazilian state of Amazonas on August 20 Reuters Amazon rainforest swept by fires: In pictures Smoke billows from a stretch of fire in the Amazon rainforest in the Brazilian state of Rondonia on 23 August AFP/Getty Amazon rainforest swept by fires: In pictures A view of logs felled illegally in the Amazon rainforest are seen in sawmills in the Brazilian state of Amazonas on August 22 Reuters Amazon rainforest swept by fires: In pictures A scorched patch of land in the state of Mato Grosso in Brazil on 20 August EPA Amazon rainforest swept by fires: In pictures Several fires are seen burning in the Amazon rainforest in this satellite image taken by NASA on 11 August AFP/Getty Amazon rainforest swept by fires: In pictures Smoke billows from a stretch of fire in the Amazon rainforest in the Brazilian state of Rondonia on 23 August AFP/Getty Amazon rainforest swept by fires: In pictures The sunsets behind clouds and smoke from fires in the Amazon rainforest in the Brazilian state of Rondonia on 18 August EPA

But he stopped well short of supporting the president's proposal, also backed by Irish Taioseach Leo Varadkar, to withhold final EU approval for the free trade agreement until Mr Bolsonaro meets environmental commitments.

The Mercosur deal, also covering Argentina, Paraguay and Uruguay, is opposed by many in France because it would expose the country's farmers to competition from large quantities of cheap beef from South America.

Mr Johnson said that he would do “everything we possibly can” to help Brazil tackle the “tragedy” of rainforest destruction

But asked whether he would join other leaders in refusing to ratify the Mercosur deal, he said: "People will take any excuse at all to interfere with free trade and to frustrate trade deals, and I don’t want to see that.

"I do want to see the tragedy in Brazil tackled properly. That’s what we need to do and that’s what the UK stands ready to support at a global level, not just in Brazil."

Boris Johnson arrives in Biarritz for the G7 summit (Dylan Martinez - Pool/Getty Images) (Getty)

Mr Bolsonaro has been accused of encouraging loggers to start fires as part of his drive to open up the Amazon region for development and of failing to direct enough resources to fight the blazes.

In a statement ahead of the G7 summit, a spokesperson for Macron said that the president believed his Brazilian counterpart had lied to him in assurances on climate made at the G20 in Japan earlier this year.