Ms Short said no human being should be more than 300 yards from a condom.

She was speaking on Tuesday at the UK launch of the World Health Organisation/UNAIDS annual report on Aids around the world.

It said 33.4 million people are now estimated to be infected with HIV, the virus that causes Aids.

Ninety-five per cent of them live in developing countries.

In some countries in southern and eastern Africa as many as one in four of the population has HIV.

"The figures we are seeing today defy belief," said Ms Short.

"How can a calamity of this magnitude and this urgency in the developing world be so totally hidden from view here?"

Major war

The Department for International Development says the number of casualties in parts of southern Africa is similar to a major war.

Ms Short called for more investment in the four main tactics she said had helped reduce the spread of HIV: condoms, education to change sexual behaviour, treatment for sexually transmitted disease and ensuring blood supplies were not infected.

She paid tribute to Uganda for its efforts in reducing the spread of HIV.

Around 10% of the Ugandan population is HIV positive, but the rate has been falling in recent months because of a huge government-backed health awareness programme.

Ms Short said a vaccine was the main long-term hope for Aids.

She claimed that the UK was the first government to support the International Aids Vaccine Initiative, set up in 1996.

It is coordinating vaccine development and looking at how developing countries might be able to afford it.

Drugs

In the West, people with HIV have been using a combination of drugs to combat the disease.

The drugs are not a cure for HIV, but they mean the disease can, in many cases, be manageable.

However, in developing countries the drugs are far too expensive, although some drug companies have begun a pilot project to offer subsidised drugs to some countries.

The Department for International Development spends £30m of its annual £250m health budget on sexual health.