The British government was yesterday accused of breaking its G8 pledge to help defeat Aids when it revealed it would only marginally increase its contribution to the Global Fund for Aids, Malaria and Tuberculosis.

The international development secretary, Douglas Alexander, promised £1bn over the next eight years to the fund, but campaigners said this fell far short of the G8 pledge to treble contributions by 2010. "This is only £125m a year. Currently the UK gives £100m a year," said Steve Cockburn, of the Stop Aids campaign.

"It is astonishing how quickly promises become meaningless. In June the G8 promised to treble the size of the Global Fund by 2010, in order to tackle three diseases that kill 6 million people each year. Then in July, at the UN, Gordon Brown claimed moral leadership by warning the world that promises to tackle poverty and disease must be not be broken. Yet today the government has done exactly that, and sadly the effect will be felt by millions of people affected by Aids, TB and malaria across the world."

The announcement at the Labour party conference comes only two days before the start of a major Global Fund replenishment conference in Berlin, where the donor countries will meet to commit new money for drugs, prevention strategies and improvements to the health services of developing countries.

Campaigners, who include Oxfam and Action Aid as well as US groups, are concerned that the low offer from the UK will have an impact on the generosity of other European nations. The German chancellor, Angela Merkel, is hosting the conference and had been expected to make a substantial increase in Germany's contribution. Beyond Europe, there are greater worries about the effect on the US. The US undertakes to provide a third of the money for the Global Fund - an amount that rises or falls according to other countries' contributions. Campaigners - including Elton John writing in the Guardian on Saturday - had called on Britain to give £700m over the next three years.

UNAIDS today raises the bar again in a report that concludes that available resources for HIV/Aids must more than quadruple from their 2007 level if the world is to achieve the goal set by the G8 of universal access to treatment for all. Some $42.2bn (£20.9bn) will be needed by 2010, it says, rising to $54bn by 2015.