Sir Keir Starmer and Volodymyr Zelensky are united in their “strong resolve” to secure a just peace in Ukraine ahead of the summit between Donald Trump and Vladimir Putin.
After a meeting at No 10, the prime minister and the Ukrainian president expressed cautious optimism about the prospect of a truce "as long as Putin takes action to prove he is serious" about ending the war, Downing Street said.
Mr Trump and the Russian president are due to meet in Alaska on Friday, raising fears the pair will try to decide the end of the war themselves, leaving Ukraine excluded and putting Europe's future security in jeopardy.
The US president said he believed Putin will make a deal, during an interview on Fox News radio on Thursday - but then later appeared to play down expectations, suggesting a second meeting involving Mr Zelensky would be more important.
As the world nervously awaits the meeting on Friday, Putin has dangled the idea that the talks could lead to Moscow and Washington reaching a deal on nuclear arms control.
After their private breakfast meeting, seen as a show of support for Kyiv, Downing Street said Sir Keir and Mr Zelensky “agreed there had been a powerful sense of unity and a strong resolve to achieve a just and lasting peace in Ukraine”.
Downing Street added there was a “viable chance to make progress as long as Putin takes action to prove he is serious about peace”.
As they entered No 10, Sir Keir embraced Mr Zelensky in front of the cameras. But the pair refused to be drawn on whether Mr Trump could be trusted.
It comes after Mr Trump threatened “severe consequences” if Putin does not agree to peace in Ukraine.
After his meeting with Sir Keir, Mr Zelensky suggested he and the PM had war-gamed potential outcomes of the Trump-Putin summit.
“We continue to coordinate our positions,” he said in a post on X. “We discussed expectations for the meeting in Alaska and possible prospects. We also discussed in considerable detail the security guarantees that can make peace truly durable if the United States succeeds in pressing Russia to stop the killings and engage in genuine, substantive diplomacy.”
He also urged Britain to join Nato's Prioritised Ukraine Requirements List initiative (Purl), which provides weapons to Kyiv, following a report that the UK is to scale back plans for a military peacekeeping force in Ukraine.
Since the weekend, Europe has rallied behind Ukraine’s right to decide its own future, amid concerns over Mr Zelensky’s exclusion from Friday’s summit.
At the weekend, Mr Trump suggested a truce could involve some "swapping" of land.
But Mr Zelensky furiously rejected any proposal that would compromise Ukraine's territorial integrity.
Putin is expected to use the summit to demand that Ukraine cede parts of the Donbas region, which it still controls.
The Kremlin said that meeting in Anchorage, Alaska, will start at 11.30am local time (8.30pm UK time).
Russia’s foreign policy adviser, Yuri Ushakov, told reporters that Mr Trump and Putin will first sit down for one-on-one talks, followed by a meeting between the two delegations. Talks will then continue over "a working breakfast”.
Following a meeting with his top officials, Putin said in a short video released by the Kremlin on Thursday that the Trump administration was making "quite energetic and sincere efforts to stop the hostilities" and to "reach agreements that are of interest to all parties involved”.
Putin also suggested that "long-term conditions of peace between our countries, and in Europe, and in the world as a whole," could be reached under an agreement with the US on nuclear arms control.
In Washington, Mr Trump said there was a 25 per cent chance that the summit would fail, but he also floated the idea that, if it succeeded, he could bring Mr Zelensky to Alaska for a three-way meeting.
He told Fox News Radio: “I believe now, he's convinced that he's going to make a deal. He's going to make a deal. I think he's going to, and we're going to find out.”
Later, while speaking to reporters in the Oval Office, Mr Trump said he would not let Putin get the better of him, adding: “He’s not going to mess around with me.”
He also highlighted the importance of a second meeting, whcih he said could also involve European leaders.
“Tomorrow [Friday], all I want to do is set the table for the next meeting, which should happen shortly,” he said.
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