A Foreign Office minister has quit following Chancellor Rishi Sunak's announcement of a cut to the UK's overseas aid spending.
Baroness Sugg resigned from her junior ministerial role after the government abandoned a Conservative manifesto commitment to fund the foreign aid budget at the equivalent of 0.7% of gross national income.
The chancellor's move has prompted fury among charities and some Tories, with former prime minister David Cameron - who wrote the 0.7% commitment into law while in Downing Street - branding it "a very sad moment".
"Putting food on people's tables, vaccinating children, stopping mothers from dying in childbirth - these were brilliant things we were doing it and it said something brilliant about this country, and it's sad we're standing back from that," the ex-premier said.
The chancellor told the House of Commons the economic crisis caused by the COVID-19 pandemic meant "sticking rigidly to spending 0.7% of our national income on overseas aid is difficult to justify to the British people".
Mr Sunak told MPs a cut in foreign aid spending in 2021 would be followed by an "intention" to return to the 0.7% commitment "when the fiscal situation allows".
In her resignation letter to Prime Minister Boris Johnson, Baroness Sugg wrote: "I believe it is fundamentally wrong to abandon our commitment to spend 0.7% of gross national income on development.
"This promise should be kept in the tough times as well as the good.
"Given the link between our development spend and the health of our economy, the economic downturn has already led to significant cuts this year and I do not believe we should reduce our support further at a time of unprecedented global crises."
She also told the prime minister that cutting foreign aid "risks undermining your efforts to promote a Global Britain and will diminish our power to influence other nations to do what is right".
Baroness Sugg had also been Mr Johnson's special envoy for girls' education.
In his reply, the prime minister said he was "very sorry" to have received the peer's letter of resignation, as he thanked Baroness Sugg for her "outstanding service".
Foreign Secretary Dominic Raab said: "Liz has been a great minister and we will sorely miss her.
"She can be proud of her record championing girls' education, promoting gender equality, supporting our Overseas Territories and the UK's vital relations in the Caribbean.
"I am sorry to see her go."
The UK is committed in law to spending 0.7% of gross national income on foreign aid every year, under legislation passed during Mr Cameron's time in office.
Mr Johnson's government is now expected to bring forward legislation to reverse that commitment.
Baroness Sugg previously served as Downing Street's director of operations and campaigns during Mr Cameron's premiership.
The ex-prime minister nominated her for a peerage when he quit Number 10 in 2016.
In an article for the Financial Times, Mr Raab described a "tough but necessary and temporary" decision to cut the aid budget.
"We take it with regret, and we will return to 0.7% as soon as the fiscal situation allows," he said.
The foreign secretary also vowed to "double down on the effectiveness of our aid".
Justin Welby, the Archbishop of Canterbury, was among those to criticise the chancellor's cutting of the foreign aid budget, branding it "shameful and wrong".
Labour's shadow chancellor Anneliese Dodds claimed Mr Sunak had "turned his back on the world's poorest".
Conservative former cabinet minister Jeremy Hunt claimed the foreign aid cut would make the UK "poorer in the eyes of the world, because people will worry that we are abandoning a noble ideal that we in this country have done more to champion than anyone else".
Fellow Tory ex-Cabinet minister Andrew Mitchell told Mr Sunak the cut would "be the cause of 100,000 preventable deaths, mainly among children".
However, other Conservative MPs were supportive of the move.
Philip Davies said people in the "real world" would support the cut, adding: "I suspect that the vast majority of the British public won't be asking why has he [Mr Sunak] cut so much, they will probably be asking why are we still spending so much."
Martin Vickers told the House of Commons he believed a "temporary move is the right one" if "we are to continue to ask our constituents to make sacrifices".