More than four in 10 charities do not maximise their Gift Aid claims, according to a report from a group of charities and charity umbrella bodies.
The group, which included the Charity Finance Directors' Group, the Charity Tax Group and the Institute of Fundraising, carried out a survey of 896 charities of all sizes, asking how Gift Aid could be simplified.
The poll found that the failure to maximise Gift Aid claims was a problem for 43.2 per cent of respondents.
"The administration involved and the complexity of the rules mean that large volumes of potential Gift Aid claims are being left unmade," the report says. "This is particularly apparent in specific fundraising situations or for events, where the rules become difficult to negotiate."
The survey found that 81 per cent of respondents favoured simplifying the process by moving to an electronic database for storing Gift Aid declarations, instead of the current paper-based system. Ninety-three per cent of organisations said they would like to be able to file Gift Aid claims online.
The main reason cited by respondents for not using online systems was that they lacked IT capability. Only 15 per cent of respondents said they would be willing to pay more than £50 for software, and 42 per cent said they would not be willing to pay anything at all, including 15 charities with incomes of more than £25m a year.
Other areas where respondents supported the simplification of current rules included auctions, entrance to attractions, sponsored events and donations through self-assessment tax returns.
Charities also said that there was a lack of understanding among donors about how Gift Aid worked, particularly people providing sponsorship for events.
"This suggests that a nationwide education campaign may be required, and that the sector needs to take a more active role in explaining the system to donors," the report says.