By David Loyn
International development correspondent, BBC News
Development opportunities have collapsed in the poorest countries
Britain will contribute to a new World Bank fund for the poorest countries, Gordon Brown is expected to confirm on Monday.
The fund calls on the richest nations to finance it with 0.7% of the money they have used to bail out the banks.
The prime minister will address a two-day conference in London a month ahead of the G20 summit of the world's biggest economies.
The conference, being billed as a "poverty summit", has been called to ensure the poorest people are not forgotten in the response to the global economic downturn.
It will include contributions from Sir Bob Geldof, as well as leaders of aid organisations and senior figures from the World Bank and World Food Programme.
Britain's Secretary of State for International Development, Douglas Alexander, will be the chairman.
He has been critical of the failure of the World Bank in the past to respond effectively at times of crisis and says the "human crisis behind the financial crisis" must be recognised.
Mr Alexander has called for an increase in the maximum amount available to the most credit-worthy countries, a swifter approval process for loans, and a more flexible approach to budget support for individual governments.
There has been a collapse in development opportunities among the poorest countries.
This has been caused by lower commodity prices, a big reduction in the amount sent home by foreign workers, the slowdown in world trade, and a cut in available credit.
At the most pessimistic end, the World Bank forecasts a shortfall in unmet financial requirements in the developing world of £497bn ($700bn) - more than the entire current aid budget.
The London conference will also look at new strategies for development ahead of a UK white paper charting an updated policy due out in July.
The paper is not expected to be radical, but the global economic downturn will force new priorities in development spending - towards more basic safety nets, and away from more nuanced policies.
For example, if there is to be mass unemployment then coping with the consequences of that will dwarf other spending demands.