Gordon Brown has backed a global campaign aimed at tackling the malaria epidemic in the developing world.
A number of countries want to buy up the vaccine
The UK has joined with other nations in buying up doses of a new anti-malaria vaccine to ensure a stable market for the drug, the chancellor revealed.
Malaria kills around 3m people each year but there have been concerns poorer nations would not be able to afford the new vaccine.
Mr Brown described the new drug as a "revolution in our time".
He told the BBC World Service Trust conference in London: "The challenge is in an area where there are insufficient purchasers with
"We need to ensure that the vaccine does go into commercial production and is available at affordable prices.
"And therefore I can announce that the British Government, working with other governments, is ready to enter into agreements to purchase these vaccines in
advance, to ensure a secure market and that the vaccines are available more
The multi-million pound investment will take place over a number of years and may include aid organisations as well as governments.
Britain expects to purchase between 200 million and 300 million doses.
The vaccine, developed by GlaxoSmithKline has few side effects and in trials in Mozambique prevented nearly 60% of cases of severe disease in children.
Each year in poor countries 500 million new cases are recorded - 90% of which are in Africa.
The majority of victims recover but the disease can damage the liver, kidneys and nervous system and up to a million of the three million fatal cases are children.
The trial of the new vaccine involved 2,022 children, half of whom were given a placebo.