With Britain staring at a fresh bout of recession, Cameron is under pressure from some members of his own Conservative party to reduce the coalition government's international aid commitment, but business leaders insisted that sticking to the funding target would not only be a "smart investment" but also the "right thing to do".
The request comes as International Development Secretary Justine Greening prepares to outline plans to boost British business involvement in developing countries.
"Aid has contributed to improving education, health, sanitation and other public services in many of the world's poorest countries. This investment in human capital is fundamental for a functioning economy," the letter said.
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Ahead of this month's budget, FTSE 100 companies like BP and GlaxoSmithKline and retailers, including Morrisons, Dixons and IKEA, joined the Premier League in putting their names to an open letter, insisting it is in Britain's interest to meet its aid pledge.
Charity leaders welcomed the support from business leaders. Justin Forsyth, Save the Children's chief executive, said, "We are delighted that some of Britain's best known companies have recognised the remarkable progress of British aid and what it is helping to achieve for the world's poorest people."