The government lacks transparency and clarity over its international HIV/Aids spending, campaigners say.
The UK has pledged £1.5bn to fight HIV/Aids over three years
ActionAid attacked the Department for International Development (DfID) ahead of a meeting to discuss the global fight against HIV, TB and malaria.
The charity said it was important to know if the money was going where it was most needed.
A DfID spokesman said the UK government had one of the best records in the world with Aids funding.
Over the next three years £1.5bn has been pledged to fight HIV.
But an ActionAid report said the department did not provide central, accurate records of expenditure and what proportion was being spent on prevention, treatment and care.
It said without such records it was impossible to tell which countries were receiving the money and whether restrictions were being placed on how it was spent.
The criticisms are similar to the findings of the Public Accounts Select Committee in April, which said UK funds were often not reaching the neediest people and DfID's approach lacked clarity.
The report has been published ahead of a London conference next week of the Global Fund to Fight Aids, Tuberculosis and Malaria, the international body responsible for distributing money.
Report author Felicity Daly said: "As one of the major donors to HIV and Aids programmes to developing countries, DfID has a responsibility for greater transparency.
"It must closely track its country-to-country aid while placing more emphasis on funding joint interventions, such as the Global Fund, that have a specific remit to fight Aids."
But a DfID spokesman said the UK had one of the best records in tackling Aids and was the second largest international donor funding HIV work in developing countries.
"DfID has always been very clear and open in its reporting of development expenditure."
Meanwhile, campaigners have called on more private and public money to be given to the Global Fund.
The fund is short of £1.6bn for 2006 and £2.3bn for 2007.
Daraus Bukenya, of the African and Medical Research Foundation, said: "One of the Millennium Development Goals is to halt the spread of HIV, malaria and TB, but how are we going to do this if there is not enough funding?"
And Stop Aids Campaign, an umbrella group of more than 70 organisations, said the London conference was the first chance for G8 leaders to "put their money where their mouth is".
Spokeswoman Judith Melby said: "The Global Fund accounts for 20% of global HIV funding.
"Donor governments need to at least double their contributions in order to close the gap between what is pledged and what is actually needed to ensure the Global Fund is effective."