The foreign aid department has said it is considering how to increase scrutiny of contractor spending after a newspaper investigation found it had soared to £1 billion a year.
Analysis of financial records from the Department for International Development (DfID) by The Times found spending on contractors from the foreign aid budget had doubled since 2012.
The newspaper said it found examples that included consultants being paid more than £1,000 a day, a UK think tank that quoted more than £10,000 to write a single blog post, and another that was given £23,000 to write a two-page document on policy.
One bank and a law firm shared £1 million to advise on Nigeria's sovereign wealth fund, while £40,000 was paid for celebrity speakers to appear at an aid conference in Mexico, The Times found.
The UK is one of only five countries to commit to a UN target of donating 0.7% of its GDP to foreign aid, totalling around £12.2 billion in 2015.
The surge in contractor spending is likely to raise concerns that taxpayers' money is flowing into private sector pay packets and projects that are bad value for money rather than helping the world's poorest people.
A DfID spokesman said: "DfID is one of the most transparent development agencies in the world and we expect the sector to adhere to the highest standards to achieve the best results for the world's poorest and value for money for the British taxpayer. UK Aid has a life-changing impact on the ground, but DfID can and will do more.
"The department is examining how we can increase scrutiny of contractor spending because if we want to defeat poverty for good, we need to improve value and impact across the aid system."
The Times analysed more than 70,000 documents disclosed by DfID that showed £38 billion of aid payouts between 2011 and 2015.
Consultancy spending reached £3.4 billion over the period, with two-thirds of contracts going to UK companies.
Justine Greening, now education secretary, was in charge at the department from 2012 to this year.
Current International Development Secretary Priti Patel has made several pledges to reform how foreign aid is spent since she took the post in July.