Former prime minister Theresa May has joined MPs rebelling against Boris Johnson's cuts to foreign aid.
The government has blamed economic damage caused by the Covid-19 pandemic for its decision to cut aid.
It expects just under £10 billion to be allocated for aid spending in 2021/22 as the prime minister plans to temporarily reduce foreign aid from 0.7% of national income to 0.5% - despite promising in his 2019 manifesto commitment to maintain spending at the higher rate.
In 2020, the UK spent £14.5 billion on foreign aid. In 2019, the figure was £15.2 billion.
Rebel MPs have criticised the decision with Conservative former chief whip Andrew Mitchell leading a push to ensure new legislation makes up the shortfall left by the cut.
The number of Tory MPs opposing the foreign aid cut doubled from 14 to 30 on Thursday - with Mrs May adding her name to the amendment.
Former foreign secretary Jeremy Hunt, former minister Caroline Nokes and ex-aid minister Sir Desmond Swayne, have backed the amendment.
Mrs May’s former deputy Damian Green and Johnny Mercer, who recently resigned as defence minister, also added their names to the amendment. The number of opposers could continue to grow.
Mr Mitchell said: “More and more of my colleagues in the House of Commons are supporting this move to to stand by our manifesto promise.
“With our economy returning to growth, there is no justification for balancing the books on the backs of the world’s poor.
“With G7 leaders coming to Britain next week, there is an opportunity for us to reclaim our rightful place on the global stage.
“Britain’s national interest is not being served by the devastating impact these cuts are already having on the ground and the unnecessary loss of hundreds of thousands of innocent lives. We urge the Government to think again.”
Ms Nokes told ITV’s Peston on Wednesday: “Women will die because of these cuts to family planning so I have joined forces with colleagues to make sure we can have a vote on it and I will be voting to keep that 0.7%.”
She also said: “I am chair of the Women and Equalities Select Committee, the cuts of 85% to family planning, the cuts to girls’ education – what we know from that is that if girls are not educated they won’t be empowered, they won’t be empowered if they are pregnant too early."
Mr Mitchell is proposing an amendment to the Advanced Research and Invention Agency (Aria) Bill, a legislation which establishes a new “high-risk, high-reward” research agency backed with £800 million of taxpayers’ cash to explore new ideas.
The explanatory note of Mr Mitchell’s amendment reads: “This new clause is intended to reaffirm the duty in the International Development (Official Development Assistance Target) Act 2015 for UK official development assistance (ODA) to amount to 0.7% of gross national income each year.
“It would require Aria to make up any shortfall in that proportion from January 2022.”
Speaker Sir Lindsay Hoyle will decide whether the amendment will be considered when the bill returns to the Commons for further consideration on June 7.
The government has also come under fire for not arranging a Commons vote on the decision to cut aid.
Asked if the amendment would be binding on the government, Ms Nokes said: “I think it’s very unclear at the moment and what we’ve seen the government do so far is what I’d describe as cuts by stealth.
“So there hasn’t been an opportunity for Parliament to express its view on this with a vote.
“I very much hope it will be binding. I don’t want to see the government try and find a way out of a commitment that we all signed up to just a few short years ago.”
Shadow foreign secretary Lisa Nandy wrote on Twitter: “On Monday, just days before world leaders arrive in Cornwall to discuss the global response to the pandemic, the Government faces defeat over its short-sighted and self-defeating decision to slash aid.
“The Conservatives should do the right thing and reverse this cut.”
Home Office minister Victoria Atkins defends the government's decision to temporarily cut foreign aid
The government has defended the cut in foreign aid saying it is a "temporary measure" because of the impact of the coronavirus.
Home Office minister, Victoria Atkins, told ITV News: "We've had to make some very difficult decisions, this reduction is one of those decisions.
"The prime minister is clear that as soon as the fiscal situation permits us to we will be returning to the 0.7% donation."