Jeremy Corbyn revealed his quintessentially British plan to change Donald Trump's mind on pulling the US out of the 2015 Paris climate accord, during a speech in York on Friday 1 June.
The Labour leader said he would invite the president to Number 10 to discuss Trump's controversial move over a cuppa. "I'd offer him some Yorkshire Tea," Corbyn told reporters, when asked how he would approach the issue.
The comment came after Corbyn described Trump's decision as "reckless and dangerous".
The populist US president said he would seek to renegotiate the agreement, which sees 187 countries vow to keep the global average temperature "well below" 2°C above pre-industrial levels.
Prime Minister Theresa May expressed her "disappointment" to Trump about the move when they spoke on Thursday, Number 10 said. But the Conservative premier failed to sign a joint statement with France, Germany and Italy condemning Trump's actions.
"Given the chance to present a united front with our international partners, she has instead opted for silence and subservience to Donald Trump," Corbyn said.
"It is a dereliction of her duty both to our country and to our planet. That is not the type of leadership Britain needs to negotiate Brexit."
Green co-leader Caroline Lucas has also described May's response as "timid".
"A true global leader would be condemning the President's actions, and joining with other European countries to formulate an emergency plan to save the Paris Agreement," she said.
"Once again we're seeing a weak Prime Minister failing to stand up tall on the world stage in the face of near-criminal behaviour from one of our closest allies.
"Britain could be leading the way on tackling climate change, and building an economy fit for the future. Instead the Tories are dragging us backwards at home, and stepping back from making an impact internationally."
The row comes just days before the UK general election on 8 June. The latest opinion from Panelbase, of more than 1,200 people between 26 May and 1 June, put the Conservatives on 44% and Labour on 36%.