Keir Starmer could head for the White House with Volodymyr Zelensky in a desperate bid to save Western alliances.
The PM is said to be ready to make the trip with the Ukrainian president and Emmanuel Macron as they try to keep Donald Trump on side.
The leaders could present a potential blueprint for peace with Russia, including an initial air and sea ceasefire, UK and French troops on the ground to guarantee security, and an American backstop.
Downing Street sources stressed nothing had been finalised, but Paris confirmed the prospect is on the table.
Defence Secretary John Healey is due in the Washington later for talks with counterparts.
At PMQs this lunchtime, Sir Keir was asked by Kemi Badenoch what he was doing to rebuild ties between the US and Ukraine. ‘She’s absolutely right that we need to do everything we can to ensure that the US, Europe and Ukraine are working together on lasting peace,’ he said.
‘I am doing everything I can to play my part in that, in regular contact with all of the key players at the moment, including talking to President Zelensky yesterday afternoon.’
The US president struck a slightly more positive tone in a speech to Congress overnight after Mr Zelensky sent him a pleading letter in the wake of the their Oval Office bust-up.
Mr Trump said he ‘appreciated’ the message, adding he wants to sign a deal for US companies to extract rare earth minerals from Ukraine. He also claimed Vladimir Putin had sent ‘strong signals’ he wants peace.
But Mr Trump stopped short of making any firm commitments, after dramatically announcing that all military aid was being suspended.
That sparked panic in Europe amid fears that Kyiv could not hold out long against Russia without American arms.
Sir Keir kicked off the session in the Commons with a veiled swipe at Vice President JD Vance, who made dismissive remarks about the security value of ‘20,000 troops from some random country that hasn’t fought a war in 30 or 40 years’.
The UK and France have both said they would be willing to put troops on the ground to guarantee a peace deal.
Mr Vance later stressed he had not mentioned the UK or France, saying both nations ‘fought bravely alongside the US over the last 20 years and beyond’. However, he did not clarify what countries he meant.
The PM said today: ‘Tomorrow marks 13 years since six young British soldiers were on patrol in Afghanistan when their vehicle was struck by an explosive tragically killing them all.’
He added: ‘These men fought and died for their country, our country. And across the wars in Afghanistan and Iraq, 642 individuals died fighting for Britain alongside our allies, many more were wounded.
‘We will never forget their bravery and their sacrifice, and I know the whole House will join (with) me in remembering them and all those who serve our country.’
Quizzed by MP on whether the US is a ‘reliable ally’, Sir Keir said ‘We work very closely with the United States on defence, on security and on intelligence. We have done for many, many years, we are intertwined, and of course they are a reliable ally. We are operating on basis day-in, day-out across the world, as he knows.’
The Prime Minister added: ‘Our main focus, our only focus, is on a lasting peace in Ukraine. There are many moving parts, there are many discussions to be had, but what I’m doing is staying focused on what I think is the single most important outcome, which is a lasting peace in Ukraine which is good for Ukraine, for Europe, and of course essential for the United Kingdom.’
In a marathon 100-minute speech Mr Trump accused European countries of spending more money on Russian oil than helping Ukraine, and blamed predecessor Joe Biden for a list of problems facing America and the world.
Mr Trump also reupped his plans to take over the Panama Canal and suggested the US would get its hands on Greenland ‘one way or another’.
As Mr Trump capped off his whirlwind first six weeks in the White House, Democrats heckled him and accused him of ‘lying’.
The US-Ukraine relationship looked on the brink of collapse after Mr Trump’s angry meeting with Zelensky last Friday, and the US President’s subsequent decision to pause military aid to Ukraine.
The dust-up also risked killing off the deal that the US and Ukraine were supposed to sign on rare earth minerals.
In his speech to Congress, Mr Trump said he was skeptical of America sending ‘billions of dollars’ to Kyiv and asked if Democrats wanted the war to ‘keep going for another five years’.
‘Wouldn’t that be beautiful?’ Trump said sarcastically. ‘It’s time to stop this madness. It’s time to halt the killing. It’s time to end this senseless war. If you want to end wars you have to talk to both sides.’
Trump said he had been in ‘serious discussions with Russia’ and had ‘received strong signals that they are ready for peace.’
He went on: ‘I received an important letter from President Zelensky of Ukraine.’
Trump then revealed that Zelensky’s letter said: ‘Ukraine is ready to come to the negotiating table as soon as possible to bring lasting peace closer. Nobody wants peace more than the Ukrainians. Regarding the agreement on minerals and security, Ukraine is ready to sign it at any time that is convenient for you.’
Trump said: ‘I appreciate that he sent this letter, just got it a little while ago.’
Turning his fire on Europe, Mr Trump said: ‘Europe has sadly spent more money buying Russian oil and gas than they have spent on defending Ukraine by far.’
Sir Keir and Mr Macron took the lead on peace negotiations after Mr Trump and Mr Zelensky’s spectacular Oval Office blowup.