Leading Aids researchers claimed this week that they are being unfairly criticised for slow progress in finding a cure for the virus. They are also concerned that the Medical Research Council has ceased to ringfence funds for Aids research.

Robin Weiss, director of research at the Institute of Cancer Research, told a Royal Society briefing: "We scientists are making fantastic progress. I cannot think of any other area of medical research where the results are pouring out at such a rate. But too much is being asked of us. Preventing or curing Aids right at the moment is beyond our powers.

"There is concern that the MRC has stopped its earmarked funding although they have said the move does not mean a reduction in funds."

Janet Darbyshire, head of the MRC clinical trials centre in London, said: "In the United Kingdom the changes to the funding arrangements have led to quite a few concerns, particularly in the basic science field."

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But Alan Stone, head of the Aids secretariat at the MRC, said funding for the research, about Pounds 15 million per year for the last few years, is expected to remain the same next year. "The MRC move has been misinterpreted by many people," he said.

The field was full of excellent research, he said, but scientists had realised that Aids was going to be "much harder to crack than some optimists had thought. People are saying 'let's stop making rash predictions'. Scientists would perhaps agree that we had been a bit simplistic or naive".

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Successes highlighted at the conference include the discovery by Oxford scientists of resistance to HIV2 in Gambian prostitutes. Dr Stone says that one of the most hopes comes from trials of chemicals that can kill HIV but are safe to be inserted into the vagina.