Anna Thomas Head of Economic and Social Development at ActionAid said: "For every pound that arrives in poor countries in aid, five pounds is removed illicitly out of the desire to evade tax.

"We work with people who have no schools for their children, no doctors and nurses when they are ill, and who don’t have enough to eat. The tax payable on capital illicitly removed would pay for services that we take for granted in the UK.

"Doha is a window of opportunity to allow poor countries to have a say in international tax regulation."

Both Christian Aid and ActionAid say upgrading the UN Committee of Experts on International Co-Operation in Tax Matters into an intergovernmental body would help end the secrecy tax havens offer.

The move is supported by more than 70 of the world’s poorest countries, but the UK Government has lobbied against it. Some 30 of the world’s 70-plus tax havens are Commonwealth countries, Crown Dependencies or British Overseas Territories.

Further UK support for havens was "apparent", the aid agencies said, when it exempted its Overseas Territories and Crown Dependencies from the UN Convention against Corruption which it signed in 2006.

This weekend’s Doha conference is to assess the progress made towards realising the 2002 Monterrey Consensus on Financing for Development, which signposted how public and private funds could be used to help poor countries.

The consensus was reached in 2002 in Monterrey, Mexico between more than 50 heads of state and 200 ministers of finance, foreign affairs development and trade, as well as heads of UN organisations, the IMF, the World Bank and World Trade Organisation.

The aid agencies said that "worrying indications" have emerged from pre-Doha negotiations taking place in New York that rich countries may block progressive measures on tax to the extent that the conference actually weakens the consensus.