Boris Johnson was told his aid cuts will lead to deaths in some of the poorest parts of the world as he faced a Tory revolt over the policy.
The Prime Minister defended the controversial move, insisting it was necessary to protect the public finances following the coronavirus pandemic.
Mr Johnson opened a crunch Commons debate on the decision to cut funding for official development assistance (ODA) from 0.7% of gross national income to 0.5%.
He said the UK’s public finances are under a “greater strain than ever before in peacetime history”, adding: “Every pound we spend on aid has to be borrowed and, in fact, represents not our money but money that we’re taking from future generations.”
However, his predecessor Theresa May said she would rebel for the first time, telling MPs the cut meant the Government “turns its back on the poorest in the world”.
“This isn’t about palaces for dictators and vanity projects, it’s about what cuts to funding mean – that fewer girls will be educated, more girls and boys will become slaves, more children will go hungry and more of the poorest people in the world will die,” the former prime minister said.
The commitment to 0.7% is written in law and was restated in the 2019 Conservative manifesto, but was ditched as the Government attempted to save money in response to the economic carnage caused by coronavirus.
The 0.5% level means £10 billion will be spent on aid this year, about £4 billion less than if the original commitment had been kept.
Despite his comfortable working majority of at least 83, Mr Johnson knows he faces a substantial rebellion in a vote which he was pressured into calling by Commons Speaker Sir Lindsay Hoyle.
A group of would-be rebels have backed a “compromise” put forward by Chancellor Rishi Sunak, which sets out tests for restoring the 0.7% level.
The funding will only be returned to the promised level if the Office for Budget Responsibility (OBR) believes the UK is not borrowing to finance day-to-day spending and underlying debt is falling.
Mr Johnson told MPs “we all believe in the principle that aid can transform lives” and voting for the Government’s motion “will provide certainty for our aid budget and an affordable path back to 0.7% while also allowing for investment in other priorities, including the NHS, schools and the police”.
“As soon as circumstances allow and the tests are met, we will return to the target that unites us,” he insisted.
Former international development secretary Andrew Mitchell said the tests to restore funding had only been met once in the last 20 years.
Mr Mitchell said the plan put forward by the Treasury was “no compromise at all” but instead “a fiscal trap for the unwary”.
“It is quite possible these conditions will never be met,” he said.
The Government was “trashing our international reputation” and the measure would have an “enormous impact on our role in the world and above all on the huge number of people who will be very severely damaged, maimed, often blinded and, indeed, die as a result of these cuts”.
He warned Mr Johnson that the cut in aid spending was damaging the Tories’ chances in seats such as Chesham and Amersham where the Liberal Democrats scored a by-election victory in June.
“Anyone who thinks this is not affecting our party’s reputation is living in cloud cuckoo land,” he said.
“There is an unpleasant odour wafting out from under my party’s front door.”
Labour leader Sir Keir Starmer also said the cut reduced UK influence around the world.
“We are the only G7 country which is cutting our aid budget,” he said.
“That is not the vision of global Britain we want to see on these benches and I don’t think it’s the vision of global Britain that many on the opposite benches want to see either.”
He warned the Chancellor’s tests would lead to an “indefinite cut” to aid spending and accused the Prime Minister of a “typically slippery” approach.
Tory MP for Thanet Sir Roger Gale said: “I shall vote today to honour our election pledge, uphold the law and restore our overseas aid spending to just 0.7% of a reduced gross national income.”
The Government has said a defeat on the motion on Tuesday would result in a return to 0.7% spending in 2022, with Mr Sunak warning that would be likely to have “consequences for the fiscal situation, including for taxation and current public spending plans”.
Tory former Cabinet minister Dame Andrea Leadsom, writing in the Daily Telegraph, backed the Treasury compromise.
“By working together to develop this compromise, I’m confident that we can move forward and focus on the overwhelmingly positive action we take in supporting the world’s most vulnerable,” she said.