The opening of an airport on the British overseas territory of St Helena has been delayed indefinitely due to safety fears - amid warnings the cost to the UK government could increase.
The £285m airport is being paid for by the Department for International Development and was due to open in May.
However, the National Audit Office said the delay - due to high winds on the remote island - could add to the cost.
DFID said it was committed to helping St Helena become "self-sufficient".
The development will provide access to St Helena for commercial airlines for the first time.
The remote island - which lies approximated 1,150 miles (1,850km) off the west coast of Africa in the South Atlantic Ocean - has previously only been accessible by ship, in a journey that takes five days from South Africa.
DFID agreed to pay £285.5m to "design, build and operate" the airport, in a bid to improve the island's accessibility and boost its tourism industry.
It hopes the development will allow the self-governing UK overseas territory to become self-sufficient and reduce its reliance on government subsidies.
In April, the St Helena government announced its opening had been postponed amid concerns wind conditions meant it was too dangerous for commercial airliners to land on the runway.
A revised date is yet to be determined. DFID and the St Helena government are currently looking at the options for dealing with the problem caused by the wind conditions but have yet to agree on a solution.
As part of the plan, the Royal Mail Ship St Helena - which provides the only regular cargo and passenger link to the island - will not be replaced once it is taken out of service, which had been due take place next month.
Sir Amyas Morse, head of the NAO, said: "Estimating the likely costs and benefits of a project such as this is an inherently difficult task, particularly with a limited number of precedents for building an airport in a remote location.
"The airport's planned opening date in May 2016 has been postponed as outstanding safety concerns are addressed, potentially adding to the project's cost and delaying its benefits."
A DFID spokesperson said: "As the report points out, the UK supports its overseas territories in line with international law.
"We are helping St Helena overcome the challenge of being one of the most remote island communities in the world so it can develop its tourism industry and become financially self-sufficient, making it less dependent on aid."