The UK's Independent Commission for Aid Impact (ICAI) warned of "serious risks" about the effectiveness of the 1.3-billion-pound Prosperity Fund for India, China, Mexico Indonesia and Brazil.
"The review calls on the government to look again at the planned rate of expenditure, including considering extending the time period over which the 1.3 billion pounds is due to be spent. It also calls on the fund to improve its transparency, saying there was too little public information available about its work," the ICAI report said.
It marks a new direction for the UK aid programme by increasing the funding available to different government departments and by focusing on middle-income countries.
"Since the referendum on leaving the European Union, the promotion of trade has been given a higher priority by the Prosperity Fund," the ICAI notes.
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The hope is that countries supported by the fund will be in a better position to trade with the world, resulting in increased economic growth, employment and prosperity.
A UK government spokesperson said: "In a post-Brexit world a more outward looking, global Britain investing and trading with the fastest growing markets is good for the UK and good for the world.
"Helping to build well-regulated, competitive markets is the right thing to do to deliver global prosperity, stability and security and help the poorest, 60 per cent of whom live in middle-income countries, to stand on their own two feet and become our trading partners of the future."