Almost one in 10 charities with annual incomes of more than £100,000 reported being victims of fraud in the financial year to March 2012, according to the Annual Fraud Indicator, published today by the National Fraud Authority.
Fraud is estimated to have cost registered charities across Great Britain £147.3m during that time, the report says. Charities reported £30m of fraud and estimated another £117m of hidden fraud, it says.
Figures from previous years have put the estimated level of fraud in the sector at between £1.1bn and £1.3bn a year.
But the NFA, which is part of the Home Office, said it had this year adopted changes in methodology that it hoped would make its estimates more accurate, such as sampling only those charities with incomes of more than £100,000 a year because they account for more than 96 per cent of sector income.
The NFA said that 1,599 registered charities responded to the third consecutive survey of the charity sector, and 9.2 per cent reported being victims of fraud in the financial year 2011/12.
Caron Bradshaw, chief executive of the Charity Finance Group, said that it remained crucial for charities to have the right anti-fraud measures in place.
"This year, the NFA has revised the methodology and the AFI figure has dropped significantly," she said. "Far from being a sign that we should rest on our laurels, this demonstrates the challenge and complexity of detecting and monitoring fraud – ultimately, so much of what we experience goes undetected.
"High levels of trust, the use of volunteers and reliance on one or only a few people to deal with finances can all present opportunities for fraudsters.
"Trust within the charity sector is an excellent thing. However, trust should always be supported by controls: the two are not mutually exclusive."