United Kingdom Prime Minister Keir Starmer was set to meet United States President Donald Trump in Washington on Thursday after having pledged to increase British defense spending in the face of what he called a "generational" security challenge.

The decision to raise military expenditure to 2.5 percent of GDP by 2027, and 3 percent by 2033, was announced on Tuesday, with Starmer saying he had "hard choices" to make in ensuring that the "defense and security of the British people must always come first".

But his decision to partly fund it by a cut in overseas aid has been criticized by charities and some members of his own governing Labour Party.

"Through those choices, as hard as they are, we must also seek unity — a whole society effort that will reach into the lives, the industries, and the homes of the British people," Starmer explained.

The timing of the announcement was notable, coming as it did just before his visit to the White House and at a time when security links between Europe and the US are under great strain.

US Defense Secretary Pete Hegseth welcomed Starmer's decision, calling it a "strong step from an enduring partner".

Trump has long been critical of European members of the NATO military alliance for not contributing enough to the communal defense budget. The current requirement, met by most members, is for 2 percent of GDP to be spent on defense, but Trump has said it should be as high as 5 percent, even though the US itself is currently only the third-highest proportionally contributing member nation, with 3.37 percent of its GDP.

According to data from the Organisation for Economic Cooperation and Development, in 2023 the UK was the world's fifth-largest international aid donor.

Writing in The Guardian newspaper, Foreign Minister David Lammy insisted the "most vital programs in the world's worst conflict zones of Ukraine, Gaza, and Sudan" would not be affected, "but there can be no hiding from the fact that many programs doing vital work will have to be put on hold".

Former Labour Party foreign secretary David Miliband, who is now head of the International Rescue Committee charity, called the aid cut "a blow to Britain's proud reputation as a global humanitarian and development leader", while Nick Dearden, director of campaign group Global Justice Now, said it was "a day of shame for Britain" with the move being taken "to appease Trump".

The United Nations children's agency UNICEF and the charity Oxfam were also heavily critical of the decision, while Labour Party member of parliament Sarah Champion, who is chair of the parliamentary International Development Select Committee, spoke out against her own party leader, saying: "Aid vs defense isn't a realistic narrative for keeping the world safe."