The Centre for Policy Studies' report calls for a review of UK aid budget and spending
Ploughing Britain's £1.4 billion EU aid contribution into the Government's international development budget after Brexit risks more waste, the Centre for Policy Studies (CPS) also warned.
International trade rather than aid cut the rate of extreme poverty from one in two to one in five people in the developing world over the 30 years to 2010, the free-market group said.
It found an increase of nearly four times in real terms of UK aid spending over the last two decades.
Many of DfID's bilateral financial programmes have been questionable.
Despite handing over £7.4 billion to the EU's aid budget since 2010, the UK has had "relatively little influence over how the money was spent".
Britain is one of just six countries to hit the United Nations' aid target, but on average the other nations ran a budget surplus in 2015 while the UK was grappling with a significant deficit.
The report said there were "worrying trends" over the amount of aid being spent on Western consultants that suggest "wasteful spending on consultants is a major issue with UK's overseas aid".
The UK is one of only six countries to meet the UN target of spending 0.7% of GDP on aid
It highlighted allegations in The Sunday Times that four executives at Adam Smith International secured £43 million in share payouts and bonuses in the four years to 2016.
Many of the Department for International Development's (DfID) programmes have been "questionable" and the Government should now review the law brought in by David Cameron setting the 0.7 per cent spending target, the CPS said.
"Overseas aid programmes can undoubtedly help lift people out of poverty, but the efficacy of aid programmes is often in doubt," its report said.
The Department for International Development has funded some 'questionable' programmes
"Even the UK's DfID – which is one of the most effective departments of its kind – faces significant challenges. Many of DfID's bilateral financial programmes have been questionable."
Brexit "provides an opportunity" for the UK to reclaim its £1.4 billion aid contribution to the EU.
"However, it is open to question whether this should all automatically be transferred to DfID's bilateral budget," the report said.
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The £1.4bn UK aid contribution to the EU may be better allocated than to the DfID, says the report
"It is hard to justify giving a department with evidence of misallocating spending an 18 per cent increase in its bilateral budget, particularly at a time when the Government will be continuing to run a substantial deficit.
"While the Government's push for more robust scrutiny of aid and for greater moves towards a more mutually beneficial overseas aid policy is welcome, it is also time for the Government to review the International Development Act that enshrines the 0.7 per cent target into law."