Gordon Brown has pledged a "significant" increase in the UK's international aid budget.

Speaking at the launch of the new Commonwealth Education Fund, he said Britain would "significantly raise our commitment to overseas development over coming years and its share of national income''.

The new fund aims to help the Commonwealth's poorest children complete good quality primary education.

Brown started the day at a south London school which links pupils with their counterparts at a school in Ghana, and later addressed the Queen and delegates at the Commonwealth Parliamentary Association's Jubilee Conference.

He pledged that every child in the Commonwealth would receive a primary education by 2015.

"There are threats we must face and defeat - from terrorism to exploitation to the easy temptations of indifference," he said.

"But before us there is also an unprecedented possibility of progress. We have in our hands the power and obligation, never given to any other generation at any other time in human history, to banish ignorance and poverty from the earth."

The government has earmarked £10 million for the project, which aims to achieve a universal primary education for children from all Commonwealth countries.

Ministers have also pledged to match pound for pound donations from business and the proceeds from a Comic Relief sports day being held later this year.

"It is a tragedy that 75 million children in the Commonwealth don't complete their basic schooling," said Brown at the initial launch last month.

"The fund can help us support work with the most vulnerable and disadvantaged children - getting street children into schooling, or helping child soldiers start a new life with counselling and education, or supporting mobile schools for nomadic children.

"It can also help promote public participation in education planning and delivery in the Commonwealth.

"The fund will ensure that more children in the Commonwealth get a decent start in life as we approach our target of primary education for all."

Aid agencies have welcomed the chancellor's move but are calling on the government to put forward a clear timetable for the introduction of new aid.

The UK spends 0.32 per cent of GDP on development aid - which is below the EU average and significantly less than the 0.7 per cent target set by the United Nations.

Dr Jenny Tonge, the Liberal Democrat shadow international development secretary, criticised the chancellor for failing to go far enough.

"The government should follow the lead of a number of other European countries, and pledge to meet the United Nation's 0.7 per cent target within the next 10 years.

"The latest figures show that rich nations as a whole are providing less development aid funding than ever before. The United States currently contributes only 0.1 per cent of its GNP, as opposed to the UK's contribution of 0.32 per cent of GNP. It is a small price to pay for a fairer world and for the extra stability which development aid provides," she said.