Sir Keir Starmer has a “very tough hand” ahead of his visit to the White House this week, John Kerry, the former US secretary of state, has told The Telegraph.

The Prime Minister will meet Donald Trump on Thursday, where he is expected to promise that Britain will “step up” and play a greater role in ensuring Europe bankrolls its own security.

One proposal could involve increasing military spending from 2.3 to 2.5 per cent of Britain’s GDP before 2030 in a move designed to appease Mr Trump, who has lambasted Europe over its defence funding commitments.

That pledge would come with significant financial difficulties.

Speaking to The Telegraph, Mr Kerry, 81, said: “The economy is obviously very challenged, and there are a lot of very tough choices in terms of budget and revenue.

“I like Keir, I think he’s a bright guy. But he’s got a very tough hand.”

‘He knows what he’s doing’

Mr Kerry, who was a senator for 28 years and ran for president against George W Bush in 2004, added that he did not want to give the Prime Minister any advice, saying: “He knows what he’s doing.”

Mr Trump called Sir Keir “a nice guy” last week, but also said that he was “not doing anything” to help end the war between Russia and Ukraine.

On Monday, Sir Keir is expected to announce a new support package for Ukraine, including military aid, despite Mr Trump piling pressure on Kyiv to back down and accept a peace deal with Russia.

Mr Kerry, who was America’s top diplomat under Barack Obama between 2013 and 2017, said: “I think the possibilities of making peace in Ukraine are real, but obviously you can’t make peace without all the parties being involved.

“Hopefully that will happen. I would assume it will happen.”