Sir Keir Starmer told to be bold with Donald Trump over Ukraine and Russia

Mr Zelensky was also branded a “dictator” by Mr Trump, something Sir Keir and other UK political figures have pushed back against.

The Ukrainian president claimed Mr Trump was living in a Russian “disinformation space” as he hit back, which led White House officials to accuse Mr Zelensky of “insulting” his counterpart.

The Americans also cancelled a planned joint press conference in Kyiv, in a sign of a deepening feud between the two countries.

Businessman Elon Musk, who is acting as an adviser on federal spending to Mr Trump, meanwhile suggested Mr Zelensky is running a “fraud machine feeding off the dead bodies of soldiers”.

Mr Musk was throwing his support behind the US president’s contested claim that Mr Zelensky’s polling popularity has fallen dramatically.

The Prime Minister will travel to America next week, to meet face-to-face with Mr Trump for the first time since he became President.

US support for Ukraine, including in enforcing peacekeeping efforts should a ceasefire be brokered, will likely be on the agenda for the meeting.

French President Emmanuel Macron is set to meet the bombastic US President ahead of Sir Keir next week.

Mr Macron said yesterday he will tell Mr Trump: “You can’t be weak in the face of President Putin.

“It’s not you, it’s not your trademark, it’s not in your interest. How can you then be credible in the face of China if you’re weak in the face of Putin?”

Calls are growing for Sir Keir to copy Mr Macron and take a hard line with the US leader, and challenge him on his claims about Ukraine and US-Russian talks on an end to the war.

Sir Ed Davey, the Liberal Democrat leader, urged the Prime Minister to speak “honestly and openly” with Mr Trump.

He added: “The threat that Donald Trump poses to our economy and security is as serious as I can ever remember.

“Whether it’s the threat of terror to our country, indeed to our friends in the Commonwealth and Europe, or whether it’s what he’s saying with President Putin and Russia and Ukraine, I think we’re all astonished and deeply alarmed, and if the British Prime Minister doesn’t reflect that, he’s not reflecting the views of the British people.”

The Lib Dem leader also urged Sir Keir to swiftly meet his commitment to raise defence spending to 2.5 per cent of gross domestic product (GDP), a measure of national economic output.

He suggested raising digital services tax on multinational companies from 2 per cent to 10 per cent would pay for the hike in defence spending.

The Chancellor Rachel Reeves said this week that she is “absolutely committed” to spending 2.5 per cent of GDP on defence.

Ms Reeves told broadcasters: “I’m really clear that a strong economy depends on strong defences and our national security being protected, so we will set out that pathway to 2.5 per cent of GDP.

“We will do it in the proper way, but no-one should be in any doubt about my commitment to spend 2.5 per cent of GDP on defence.”

Defence Secretary John Healey reasserted the pledge that Nato countries will “do more”, while on a visit to Norway.

Speaking at a press conference alongside his Norwegian counterpart Tore Sandvik, the Rawmarsh and Conisbrough MP said that Russian leader Vladimir Putin wants to “divide Nato”.

He added: “In the last year, the non-US nations of Nato increased defence spending by 20 per cent, so we are stepping up on European security.

“We recognised in the discussions that I chaired earlier this week in Nato that we must do more, and we will.

“That isn’t just about how much you spend. It’s about how you spend it.

“And Nato also needs nations like Norway, like the UK, ready to set new standards of how we work together, we plan together, we deter together and if necessary, we will fight together.”

Mr Healey was speaking after European nations met earlier this week in a scramble to boost their defence spending after pressure from the US.

American and Russian officials, meanwhile, met in Saudi Arabia for initial talks on ending the conflict, without any Ukrainian representation.

But speaking after a G20 meeting of foreign ministers in Johannesburg, South Africa, Foreign Secretary David Lammy cast doubt on Moscow’s willingness to negotiate seriously.

He said: “We’ve not got anywhere near a negotiated settlement, and I have to say when I listened to what the Russians and what (Russian foreign minister Sergei) Lavrov has just said in the chamber this afternoon, I don’t see an appetite to really get to that peace.”

Both Mr Lammy and Mr Lavrov gave speeches in a behind-closed-doors session in Johannesburg.

The text of Mr Lavrov’s speech has not been released and it is understood the Russian foreign minister boycotted Mr Lammy’s speech.

According to a copy of Mr Lammy’s remarks posted on the Foreign Office’s website, he accused his Russian counterpart of advancing “tired fabrications” and urged Moscow to abandon “tsarist imperialism”.