Gordon Brown and leaders of all the main religions will announce a £2.1 billion programme today to immunise 500 million children over the next decade.

For the first time, Britain and other governments are selling “aid bonds” to the international money markets, raising money for the developing world now and paying back the interest from future aid flows. The bonds are a way of front-loading aid promises made by governments over the coming decade, making it possible to spend more of the money earlier.

The Chancellor devised the International Finance Facility for Immunisation to raise the money from financial institutions to fund a mass immunisation programme against polio, measles, diphtheria and hepatitis in the world’s poorest countries.

The Government says that spending the aid money earlier makes it more effective because it saves the long-term costs of dealing with disease once it arises.

It cites the example of smallpox, which was eradicated in 1980 after a 15-year, $300 million (£158 million) campaign lead by the World Health Organisation. It is estimated that the US saves the total cost of all its contributions every 26 days.

The Chancellor will present the religious leaders, including the Archbishop of Canterbury, Dr Rowan Williams, with €1,000 (£670) bonds — government-backed IOU notes — that they are buying to show support for the initiative.

The Pope, represented by Cardinal Martino, will buy the first bond, the first time that the Vatican has made a gesture of its type. Other bonds will be bought by Dr Jonathan Sacks,the Chief Rabbi, the Muslim Council of Britain, the Hindu Forum and the Network of Sikh Organisations. The money raised from the bonds will be used to immunise 500 million children across the world’s 70 poorest countries by 2015. It is hoped that the campaign will save 10 million lives and help to eradicate polio.

It costs £20 to immunise a child but it is estimated that each year 27 million children go without vaccination, leaving them vulnerable to prevent- able infections. As a result, 2.5 million children under the age of 5 die unnecessarily each year — about one child every second.

The worldwide vaccination programme is being co-ordinated by the Global Alliance for Vaccines and Immunisation, which is co-founded by the Gates Foundation. Its aim is to ensure that every child in the world receives vaccinations.

A spokesman for the alliance said: “You double the number of lives saved than you would if you spend the money year after year. It is a lot more effective.”

Mr Brown will say: “Millions of people campaigned to make poverty history last year, and now we can say to them all: we are delivering the promises we made, your hopes are becoming a reality and millions of young children’s lives will be saved as a result.”

More than £1 billion has already been committed by donors, and Britain is leading the way with a £7.3 million commitment.

Goldman Sachs and Deutsche Bank, the merchant banks that are managing the scheme, started receiving bids from bond traders yesterday morning and will stop taking the bids at 7am today.

The bonds, which are underwritten by the World Bank, will then be traded on the open market, with the price depending on the level of bids received.

The first bond will be represented to the religious leaders at the ceremony today, which will also be attended by Queen Rania of Jordan and the pop stars and anti-poverty campaigners Bono and Bob Geldof.

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