Boris Johnson has been warned not to push Britain into a “Trump first” Brexit, as he heads for his first face-to-face meeting as prime minister with the US president at the G7 summit of world leaders in France.

The PM hopes to use the gathering in Biarritz to promote his vision of a post-Brexit UK as an “international, outward-looking, self-confident” nation playing a leading role in global affairs.

Speaking ahead of the three-day summit, he said it would be “gravely mistaken” to believe that the UK will retreat from the world stage as a result of leaving the EU, promising it will continue to make its voice heard on issues ranging from climate change to the defence of democracy and human rights.

“We will be an energetic partner on the world stage,” he said. “We will stand alongside our G7 allies to solve the most pressing international issues.”

But Labour leader Jeremy Corbyn warned that in reality Mr Johnson’s eagerness for a US trade deal will deliver the “ugly spectacle” of a British prime minister putting the country “at the mercy of a US administration that threatens peace, prosperity and the future of our planet”.

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The summit in the Basque beach resort is set to be dominated by anger over the destruction of the Amazon rainforest, after host Emmanuel Macron declared the spate of wildfires in the region an “international emergency” and threatened to block a trade deal between the EU and South American economic bloc Mercosur unless Brazilian president Jair Bolsonaro acts.

But the highlight for Mr Johnson in his first outing on the global stage will be early-morning talks with Trump on Sunday, expected to last up to an hour and to focus on post-Brexit trade.

The pair spoke on the phone on Friday evening ahead of their meeting, their fourth official phone call since Mr Johnson took office a month ago and the second call this week.

A Downing Street spokesman said: “They discussed topics on the agenda for the summit, including foreign policy issues and global trade.”

Preliminary discussions have already thrown up potential obstacles to a wide-ranging deal, including US pressure to open up British markets to agricultural produce such as GM crops and chlorine-washed chicken. Mr Johnson has promised MPs that ”under no circumstances” would NHS contracts be opened up to US firms.

Trump’s envoy John Bolton suggested last week that mini-deals in areas like cars or manufacturing could be swiftly agreed, leaving more contentious issues to be thrashed out over the longer term.

But the UK Is understood still to be aiming for a comprehensive deal, and to be ready to accept delay as the price of getting it right.

A UK government spokesperson said: the PM and president were committed to starting negotiations as soon as possible on an “ambitious” free trade agreement, adding: “Of course we want to move quickly, but we want to get the right deal that works for both sides.”

Mr Johnson will also have bilateral discussions with leaders of Canada, India, Australia, Japan and Egypt as he seeks to foster trade deals elsewhere in the world following the UK’s self-exclusion from the European single market.

He faces awkward conversations with Trump over Iran, where the UK has so far stood firm alongside EU allies France and Germany in resisting US pressure to reimpose sanctions lifted in the Obama-era nuclear deal

Donald Trump (Reuters) (REUTERS)

The UK is set to try to avoid clashes in Biarritz by highlighting the trans-Atlantic allies’ unity behind the shared objective of preventing Iran from obtaining nuclear military capabilities and reining in its destabilising activities in the Middle East, rather than foregrounding differences between the US and Europe over tactics.

Mr Johnson will also make clear his view of the importance on delivering on climate change goals set out in the 2016 Paris Agreement. Rather than seeking confrontation with Trump over his decision to pull the US out of the accord, he is expected to encourage and cajole the president to press ahead with domestic measures to cut greenhouse gases.

The PM’s trips to Berlin and Paris ahead of the summit have largely taken Brexit out of the spotlight at Biarritz, though he will hold his first face-to-face talks with European Council president Donald Tusk at which he will press for fresh talks about possible alternatives to the Irish border backstop following indications from Angela Merkel and Emmanuel Macron that they are ready to listen to UK proposals.

Anti-poverty demonstrators in Biarritz (AFP/Getty)

Mr Johnson rejected suggestions that the UK’s role in the world will be diminished by Brexit, saying: “Some people question the democratic decision this country has made, fearing that we will retreat from the world. Some think Britain’s best days are behind us. To those people I say: you are gravely mistaken.

“We will stand up for liberty, democracy, the rule of law, equality and human rights – the ideals that we share with our friends and allies.

“We will remain at the heart of the alliances that span the world. And we will continue to use the breadth of our expertise in diplomacy, defence and development to uphold and safeguard the global order on which peace and prosperity depends.”

But Mr Corbyn said that the G7 group of rich countries were “key drivers of global inequality” as well as having a major responsibility for the climate emergency.

“The UK should use its position in the G7, on the UN Security Council and the international financial institutions to promote policies to tackle the climate emergency and that are proven to reduce inequality and improve lives around the world, including universal healthcare, education and social security,” said the Labour leader.

“Instead, this weekend we’ll see the ugly spectacle of our prime minister pursuing his Trump first policy, putting us at the mercy of a US administration that threatens peace, prosperity and the future of our planet.”

Jeremy Corbyn (AP)

CBO deputy director-general Josh Hardie warned that the Biarritz summit came at a time when “the global economy is stuttering and our international trading system is under unprecedented pressure”.

“Damaging trade wars, the threat of a no-deal Brexit and the uncertain future of the World Trade Organisation are hindering business efforts to deliver prosperity and growth,” said Mr Hardie.