Labour leader Jeremy Corbyn says any Donald Trump trade deal brokered by Boris Johnson would be a threat to the climate.
Unveiling plans for 10 new national parks and a radical plan to plant two billion trees to tackle the climate emergency, Mr Corbyn said leaked documents showed US officials wanted no mention of the effects of global warming.
He said the documents - first disclosed by Labour to expose an alleged plot to sell off the NHS - showed "US negotiators complaining about our controls on pesticides".
Mr Corbyn added: "They’ve even attacked our basic rules on consumer labelling including for controversial genetically modified crops. But one thing the US government absolutely refuses to discuss is the climate crisis."
Mr Corbyn, speaking in Southampton, went on: "US officials are 'emphatic' that they will, and I quote 'not include mention of greenhouse gas reductions in trade agreements' because climate change is, they say, 'very sensitive in the US'.
"Well, I don’t care how sensitive it is, this is the biggest threat to our future.
"There could scarcely be more of a contrast between the complacency and denial of Trump and Johnson and the urgency of the younger generation whose future is at stake."
A Labour government will create ten brand new National Parks, he said, increasing the total size of our National Parks by 50% meaning three-quarters of people will live within 30 minutes of a National Park.
Obvious candidates, he went on, include: the Cotswolds, the Chilterns, the North and South Pennines, Coastal Suffolk, Coastal Dorset, and the Lincolnshire Wolds.
He has committed to spending £3.7 billion in capital investment for the planting programme and habitat restoration if he wins the election.
Friends of the Earth welcomed the planting plan as “by far the most ambitious” of all the parties’ tree pledges, which are aimed at capturing atmospheric carbon to offset emissions.
Environmental degradation, potential for carbon sequestration and biodiversity net gain would be among the criteria for the areas to get the status.
Labour estimates the programmes would help create 20,000 of the one million green jobs it has pledged as part of a “green industrial revolution”.
While the plans focus solely on England, Labour wants to work with the devolved governments of Scotland, Wales and Northern Ireland to ensure “nature recovery networks” are extended across the UK.
The Liberal Democrats have pledged to plant 60 million trees a year, equating to up to 1.2 billion by 2040, while the Tories have pledged half that.
"In parts of our country the air we breathe is poisoning us," added Mr Corbyn.
"Air pollution contributes to more than 40,000 deaths a year. The number is staggering."
Labour will introduce a new Clean Air Act, encouraging cleaner transport and clean air zones around our children’s schools.
Commenting on Labour’s announcement, Friends of the Earth tree campaigner Guy Shrubsole said: “This is by far the most ambitious tree-planting pledge we’ve seen from a political party.
“Tree cover in the UK needs to double as part of the fight against climate breakdown and this means adding three billion new trees, and fast.
“If sustained, Labour’s promised tree-planting rates would achieve this by 2050. While parties have been racing to make bigger trees pledges, it’s crucial to remember that trees will only help fix the climate crisis if emissions cuts happen at the same time.”
Labour said £1.2 billion from its green transformation fund would be spent on restoring natural habitats including woodland, grasslands, meadows, peat bogs and salt marshes in England.
A further £2.5 billion from the fund would be available for tree planting in national parks and in the National Forest as well as in publicly owned land such as parks and schools and in farmlands.
Watch Jeremy Corbyn's full speech below: