His intervention came ahead of the launch by the prime minister next Tuesday of the government’s own #1.5bn Aids plan. “We work with the Americans in a whole variety of ways, but we have a difference of view on abstinence-only campaigns,” said Mr Thomas.

The Bush administration pledged $15bn (#8bn) to Aids over five years, but the vast bulk will go to programmes that stress abstinence. The ABC policy  for Abstinence, Be faithful and Condoms “where appropriate”  sits relatively comfortably with the religious right in the US and the faith groups working in the developing world who tend to be the Americans’ chosen partners.

The Blair plan will focus on the reproductive rights of women and their need to protect themselves, recognising abstinence is frequently not an option in some of the worst-hit parts of the world, and that husbands are unfaithful.

The UK is a big funder of condoms, paying for 490m of the 1bn distributed in the developing world, and that, said Mr Thomas, “is not enough if we are to make an impact in preventing the spread of HIV/Aids”.

He emphasised that the UK would continue to back the “excellent HIV, sexual and reproductive health work” of the UN Population Fund and the International Planned Parenthood Federation, both of which had their funding slashed by the Bush administration because they support sexual health clinics for women that include abortion services.

Ten days ago, Britain’s Department for International Development announced #116m for UN Aids organisations, and in March it gave #12m to the federation.

The UK will also not side with the US over the use of cheap generic drugs made in developing countries such as India, which the US government refuses to accept are high quality  even though they have been evaluated and approved by the World Health Organisation. The drugs are copies of medicines under patent to the world’s biggest and richest pharmaceutical companies, most of which are based in the US. Campaigners point out that generics are far cheaper and will save more lives.

“One of the reasons we work with the international community is that we think the WHO and other organisations have the technical expertise so that countries through their ministries of health can make the decisions they want to about the drugs they use,” said Mr Thomas.

The third point of conflict is over the Global Fund for HIV/Aids, Tuberculosis and Malaria which channels money from donors into programmes drawn up by developing countries. The Bush government has given only $500m of its $15bn to the fund, preferring to run its own projects. The chancellor, Gordon Brown, announced an unprecedented #1.5bn for Aids relief on Monday. Next week Mr Blair will announce that a substantial chunk will go to the Global Fund.

Last night Nelson Mandela came out of retirement to make a public appeal for more money for the fund. At an evening event where the Bill and Melinda Gates Foundation announced it would give another $50m, Mr Mandela called for substantially increased donations, as well as commitments to the fight against the pandemic. “Our inability to act decisively on this challenge is a direct reflection of our disregard for our common humanity,” he said.

“Let me say this as directly as I can: HIV/Aids is the real enemy,” he said. “The denial, stigma and complacency that fuel HIV/Aids  these too are the real enemies. It is morally imperative that we direct our energies at these enemies, not at one another.

“We may not agree on every tactic employed by every donor and we may have passionate opinions about how things can be done better, but we must work with each other to find the best solutions, while knowing that every person in this fight simply wants to save lives. That is a noble calling and should be appreciated and respected.”

Demonstrators delayed Mr Tobias’s presentation, chanting “Bush lies, people die.” He declined to go to the podium until the placards in front of him stating “He lies” were lowered. But he did not duck the controversial issues. He cited the Ugandan president, Yoweri Museveni, in support of the US “ABC” policy  abstinence, be faithful and condoms  “where appropriate.”

Mr Tobias said: “When we say we are listening, and we say those on the ground know best, then we must surely listen and learn from the man who has led one of the most successful and pivotal battles against this disease. Yoweri Museveni has, largely by sheer leadership and will, fought back this disease in his country with an ABC prevention focus.

“We must learn from his leadership in the fight against Aids. Abstinence works  being faithful works  condoms work. Each has its place.”

The UN agencies have all expressed their doubts about abstinence and fidelity, pointing out that women in southern Africa often do not have the power to say no and that married women are more likely to be infected with HIV, via their unfaithful husbands, than unmarried women.

“There is an urgent need to rethink the ABC approach,” said Thoraya Obaid, executive director of the UN’s Population Fund, at the launch of a report which outlined the dire plight of women in southern Africa, who make up 57% of those now infected and unable to protect themselves.

But Mr Tobias said there was confusion about the US position and there was no right answer to preventing the spread of Aids. “Those who want to simplify the solution to just one method, any one method, do not understand the complexity of the problem,” he said.

The US president’s emergency plan for Aids relief (Pepfar) would work with local people in affected areas, he said, giving money directly to groups in the communities who would know best what worked for them.

Mr Tobias, who has expressed doubts about the quality of the generic Aids drugs made in India, said if the drugs were submitted for approval by the US drug regulators, they would be eligible for US purchase “so long as international patent agreements and local government policies allow their purchase.”

The US has been criticised for failing to put more money into the Global Fund for HIV/Aids, Tuberculosis and Malaria, which funds programmes put forward by developing world governments. The fund was “a young venture and still maturing”, Mr Tobias said, but “a very promising vehicle and a critically important part of the work that all of us are doing.”

“Making certain countries drop these measures in the framework of bilateral trade negotiations would be tantamount to blackmail, since what is the point of starting treatment without any guarantee of having quality and affordable drugs in the long term?” Mr Chirac wrote in a statement that was read to the International AIDS conference in Bangkok yesterday.

Although the president did not name the Bush administration in his attack, French officials later explicitly named the U.S. as being at the heart of the problem.

Mireille Guigaz, France’s global ambassador on AIDS, said: “It is a question between the United States and developing countries, and the way  the U.S. wants to put pressure on developing countries who try to stand up for their own industries. We do not wish countries’ hands [to be] tied by bilateral agreements.”

The U.S. has been pursuing bilateral trade agreements expected to close the loophole allowed by the World Trade Organisation’s agreement on drug patents last year. At Doha, it was agreed that poor countries in need of medicines could disregard the 20-year patents on new drugs owned by the multinational drug companies, most of which are based in the US.

The deal, completed at Cancun, lets poor countries buy cheap, generic copies of patented drugs from the makers, in India, Brazil and Thailand. AIDS drugs were hugely expensive before such firms made their copies and brought the prices down from $10,000 (#5,400) a patient a year to under $300 (#162).

According to the World Health Organisation, 6 million people in poor countries need antiretroviral treatment but only 440,000 are getting it.

On Monday, a report from Oxfam warned that bilateral agreements were set to do great damage to the fight against AIDS in Thailand, where the government has so far been able to administer generic versions of AIDS drugs made by its own government pharmaceutical organisation (GPO). Thailand has said it intends to export its copies to neighbouring countries.

But the U.S. launched negotiations on a free trade agreement with Thailand on June 30. Similar agreements, signed by the U.S. with Singapore, Chile and central American countries, contain stringent intellectual property provisions, according to Oxfam. If Thailand is forced down the same road, its government may not be able to license the GPO to make new, cheap AIDS drugs as the older ones lose their efficacy.

The agreements already signed extend patent protection beyond 20 years, Oxfam said, and limit a government’s ability to allow its own generic companies to make copies of patented drugs and import generic versions. “Oxfam shares the concerns of Thai NGOs that a free trade agreement with the US, containing unnecessarily high intellectual property standards, will seriously undermine future access to affordable medicines in Thailand,” the report says.

Xavier Darcos, the French minister for cooperation and development, said France wanted to see a global agreement on access to medicines and favoured any that allowed “the countries in most need to access drugs, ideally free, or else produce them.”

Mr Chirac, in his statement, also called for the U.S. to put more money into the Global Fund for HIV/AIDS, Tuberculo sis and Malaria. “We should ensure the sustainability of the fund’s financing and raise its resources to $3bn a year by sharing this effort among Europe, the United States and all the other donors.”

The UN secretary general, Kofi Annan, said he thought that the U.S. contribution of $500m to the global fund should have been $1bn of the $15bn the Bush administration had pledged for AIDS projects.

Yesterday the UN said there would be 50 million orphans in sub-Saharan Africa by 2010, of whom 18.4 million would have lost one or both parents to AIDS. Yet it was a crisis that had been ignored. A report from Unicef, the children’s fund, revealed that from 2001 to 2003 the number of children worldwide orphaned by AIDS rose from 11.5 million to 15 million. Most of the AIDS orphans were in Africa, which has been hardest hit by the pandemic.

o Josi Manuel Barroso, the president-designate of the European commission, yesterday attacked American “arrogance” but insisted the EU had to keep good relations with the US. The former prime minister of Portugal, who backed the Iraq war, said he admired the nation but he hated “their arrogance, their unilateralism”, But it was very much in Europe’s interest “to try to have a constructive relationship.”

Although the numbers on treatment have gone up by more than half, to an estimated 440,000, and the number of pregnant women being tested for HIV has doubled to 5.5 million, with 71,000 receiving drugs to avoid passing the virus to their baby, the gains are small in proportion to the scale of the need, says UNAids.

Only 3.6% of injecting drug users in 2003 had access to help to avoid HIV infection or to treatment. Even condom provision is too low  12bn are needed each year for protection from the virus, but of the 6.9bn used last year, only 2.7bn were used for disease prevention. The one real gain was in Aids education, available now to about half of all secondary schoolchildren worldwide and two-thirds in Africa.

The picture is not clear on support for orphans, but statistics from national governments suggest that about 700,000 are receiving some sort of state help  probably only 5% of the total.

“Access to these and other prevention and care services still falls far short of the millennium development goals,” said John Stover of Futures Group International, one of the authors of the reports.

Much more money is needed to step up the response to the pandemic, says UNAids. In 2001 the UN special session in New York called for $9.2bn (#4.9bn). UNAids has now increased that estimate to $12bn by 2005, and $20bn by 2007.

Of the $20bn, it says, $10bn is needed for prevention, $7bn for treatment, $2bn for orphan care and $1bn for policy, advocacy and administration. The estimate includes drug treatment for just over 6 million people  around 52% of those who will need it by then.

But the chances of raising that level of funding look remote. This year $6bn will be available when the need is $8bn. In 2005, UNAids predicts that $8bn will be raised of the $12bn needed. By 2007 there will be a 50% shortfall, with only $10bn of the required $20bn forthcoming.

“There is an increasing gap between what is needed and what is available,” said Paul DeLay, director of evaluation at UNAids.

Earlier the Ugandan president, Yoweri Museveni, said he doubted that promoting condoms over abstinence was the best method of preventing HIV infection.

“The principle of condoms is not the ultimate solution,” said Mr Museveni. It was important that loving relationships were based on trust. “Let the condom be used by people who cannot abstain, cannot be faithful or are estranged.”

The president is widely admired for his leadership in confronting the Aids epidemic in Uganda and bringing the infection rate down through public education campaigns.

But his remarks surprised many by chiming with the US philosophy of ABC  abstinence, be faithful and (lastly) condoms. Many who work in HIV/Aids in Africa say abstinence is not possible for women, whose first sexual experience is often young and forced.

Tim Brown of the East-West Centre in Hawaii, which is involved in mapping the epidemic, disagreed.

“Condoms are greatly short-changed in Africa as a prevention method,” he said. “If you increase condom use by 50%, I guarantee you that HIV will go down by 50%.”

The Department of Health and Human Services, headed by the health secretary, Tommy Thompson, was yesterday accused of actively preventing certain US scientists and doctors who had a contribution to make from travelling to Bangkok.

Many suspect that behind the action lies a rift between the US and AIDS activists who oppose America’s approach to the global pandemic.

Joep Lange, president of the Sweden-based International AIDS Society, which organises the conference, said it had been forced to retract papers that had been accepted for conference sessions after the US scientist authors had been refused permission to come. Many meetings, some to train developing world researchers, have had to be cancelled.

“I really think it is shameful that they restricted the US government participation, particularly when you think they are putting so much money into the fight and people in the field who have to do the job are directly prevented from coming here,” said Dr Lange.

Earlier, the editor of the Journal of the American Medical Association (Jama) had also unexpectedly spoken out. Catherine DeAngelis said that Marc Bulterys, the co-author of a Jama paper who worked for the government’s Atlanta-based Centres for Disease Control (CDC), had not been allowed to accept an invitation to fly to Bangkok to talk about it.

“It stymies the ability of scientists to discuss and learn from each other,” said Dr DeAngelis. “It is wrong.”

She pointed out that the trip would have been paid for by the American Medical Association, not the US government. “It is an incredible example of political pettiness. It is anti-intellectual and it is interfering with scientists and the scientific process and means American government-employed scientists are not allowed to be here to share their knowledge,” she said.

Behind the fracas lies the gulf between the US policies on tackling HIV/AIDS in the developing world and those of AIDS activists who tend to dominate the big international event. Two years ago, Mr Thompson tried to give a speech at the conference in Barcelona but was rendered inaudible by noisy protests. This year the organisers have asked activists to be more civil and allow those with whom they disagree to be heard.

Although the US has put more money into the fight against HIV/AIDS than the rest of the world put together, including $15bn (#8.5bn) pledged by President Bush in January last year, activists are unhappy with the way the money is to be spent. Most of it will go to American-instigated programmes in 15 selected countries which stress the so-called ABC philosophy  abstinence, be faithful and condoms “where appropriate”.

Peter Piot, executive director of UNAIDS, said last week that abstinence, particularly for women in southern Africa, was often not an option.

Randall Tobias, the former head of the pharmaceutical firm Eli Lilly, who runs the president’s plan for AIDS relief, heads the US team in Bangkok. Yesterday he said he had “a very large delegation” with him.

The CDC had offered another scientist instead of Dr Bulterys, he said. “It is true that the person who was the author was not part of the delegation but we offered another scientist and they declined,” he said.

The significance of the conference was emphasised at the opening ceremony by Joep Lange, president of the International AIDS Society. The Bangkok event is the first in the AIDS-hit developing world since the conference in Durban, South Africa, in 2000.

“Durban was a watershed event that catalysed many developments,” he said. Prices of AIDS drugs came down, fundraising was stepped up and there are now plans to put millions on treatment.

“Like Durban, Bangkok could be a watershed event,” he said. “The conference is strategically located in Asia, the most populous continent in the world and home to a quarter of all new HIV infections. Asia still has the opportunity to prevent the epidemic from getting completely out of hand.”

Kofi Annan, UN secretary general, called for leadership from all parts of governments, all the way to the top, which has not been seen in all Asian countries, just as African leaders took years to recognise the crisis and speak out against stigma. “AIDS is far more than a health crisis. It is a threat to development itself,” he said.

Leadership was one of three priorities he defined. He also called for infrastructure to be scaled up in AIDS-hit countries to allow more people to be treated and he called for a better deal for women who are unable to defend themselves against unsafe sex because of poverty, abuse, violence and coercion by older men. “What is needed is the education of girls,” he said.