The UK has cut this year’s aid to the UN agency that fights AIDS and HIV by £12.5m – more than 80% – in a move condemned as "shameful" and "maddeningly short-sighted".
Funding has fallen to £2.5m from £15m in 2020, UNAIDS said.
It is the latest in a drip-drip of revelations about the impact of Boris Johnson‘s decision last November to reduce the UK spending target for overseas aid to 0.5% of national income from 0.7% in the face of fierce opposition from MPs and aid agencies.
The drop translates into a reduction of more than £4bn in the overseas aid budget.
The government has said the "seismic impact" of the pandemic forced it to take "tough but necessary" decisions. It remains one of the world’s largest overseas aid donors.
News that global efforts to combat AIDS and HIV would be affected by the cuts triggered an outcry among campaigners, in particular as they come in the year when Britain takes a lead role on the world stage, hosting a G7 summit of powers and a UN climate change summit.
UNAIDS said the cut is "significant", adding: "It affects the provision of live-saving HIV prevention and treatment services around the world.
"It affects the empowerment of young women and adolescent girls and their access to sexual and reproductive health and rights across the world, and Africa in particular.
"It impacts on support to upholding the human rights of some of the most marginalised people, including lesbian, gay, bi-sexual, transgender, queer and intersex people in low- and middle-income countries. It reduces global health security.
"UNAIDS recognises the challenging situation facing many governments, yet deeply regrets this decision of our longstanding partner and advocate. We are assessing the full scope and impact of the cut and are actively formulating mitigation strategies.
"The UK government has said the decision does not reflect a diminished commitment to UNAIDS or the HIV response. UNAIDS will continue working with the UK and partners to explore ways to ensure continuity and predictability of funding to sustain the hard-won gains in the fight against HIV and to end AIDS as a public health threat by 2030."
Saoirse Fitzpatrick, advocacy manager at STOPAIDS, a network of some 70 organisations, said: "These shameful cuts to HIV funding risk abandoning the UK’s leadership and influence within the HIV response at a pivotal moment.
"These cuts will hit the most marginalised communities around the world hardest. It threatens to undo decades of progress made in the HIV response that UK Aid has made possible.
"With 690,000 people dying from an AIDS-related illness each year, the UK government must urgently change tack and protect its funding for UNAIDS and other organisations doing vital work in the HIV response."
Christine Stegling, executive director at the charity Frontline AIDS, said: "For the first time in decades, there is a very real threat of hard-won progress on HIV and AIDS going into reverse.
"These cuts by the UK government will actively increase that risk, setting the stage for a surge in HIV rates and AIDS deaths across many countries.
"The UK government might also reflect on the fact that HIV, much like COVID-19, doesn’t recognise borders. An increase in rates in any country should and will eventually become an issue for every country. A maddeningly short-sighted decision."
The cuts in UK funding to UNAIDS were first reported by Will Worley, a journalist for the website Devex, which covers the global development sector.