The two professors say that Mr Brown's announcement that the government would pre-buy 300m doses of a vaccine being developed by the British drug company GlaxoSmithKline at a cost of £3bn to the taxpayer is a misguided good intention.

"Malaria really can and should be conquered - and we now have the necessary tools to do the job," they write. "We are concerned therefore that while millions of people suffer every year, you are proposing allocating precious funds to a future uncertainty."

Nick White, professor of tropical medicine at Bangkok and Oxford universities, and Bob Snow, professor of tropical public health at the Kenyan Medical Research Institute, Nairobi, and Oxford University, say that simple interventions such as free bed-nets to keep malarial mosquitos away from children at night and new but cheap drugs based on the artimisinin plant grown in China could eliminate malaria from parts of the world where there is low transmission, such as South Africa, Angola and northern Kenya. This would allow a more intensive focus on the bigger problems in other places, such as India and Burma.

They applaud Mr Brown for recognising malaria "as a major cause of poverty, suffering, and death in the developing world" but question the promise of funding for a vaccine which he made 10 days ago, just after publication of GSK's trial results in the Lancet. These showed that the vaccine worked in 30% of a small group of children in Africa, though as yet nobody knows for how long.