Christian Aid is asking supporters to get behind a new online campaign to end the tax injustices it says are keeping developing countries locked in poverty.

Supporters are being asked to email their local MPs to encourage them to lobby Prime Minister Gordon Brown on the secrecy surrounding offshore banking.

Christian Aid accused multinationals of “aggressive” tax avoidance and of using “creative accounting” to reduce their tax liabilities by hiding their true profits in off-shore accounts.

Tax avoidance, it said, is costing developing countries an estimated $160bn, almost double the amount that they receive in aid.

Christian Aid said that the amount of wealth being lost “by the back door” meant developing nations had to rely on aid instead of being able to provide basic services like education and healthcare by themselves. It claims that the lives of 350,000 children under the age of five could be saved each year if developing countries had the lost taxes to invest in development.

The aid agency is calling for new rules that would force multinational companies to reveal their profits and the amount of tax they are paying in each country where they operate. It wants to see Mr Brown press other world leaders for country by country reporting at the forthcoming G20.

Matthew Sowemimo, Christian Aid’s tax campaign officer, is appealing to people to email their MPs.

“We are asking supporters to get their MPs involved. When an MP writes to the Prime Minister, he or she has to receive a personal reply,” he said.

“We are confident that a lot of MPs will support this and that Gordon Brown will be shown the strong support that exists for real reform.

“It will take a couple of minutes and could change the world,” he said.

On the web: www.christianaid.org.uk/tax