Fundraising websites should feature "broad explanatory guidelines" for donors about charity registration and Gift Aid, according to the Institute of Fundraising.
The call for clarity comes because of questions about the way the fundraising websites Bmycharity and JustGiving describe unregistered charities or Community Amateur Sports Clubs, which get charitable tax advantages, on their websites.
CASCs, charities that have an incomes below £5,000 a year and those that fall into the 'excepted' or 'exempt' categories do not have to register with the Charity Commission but need to be accredited with HM Revenue & Customs to claim Gift Aid.
Bmycharity has adopted a policy of allowing only registered charities to use the site, and its trustees are considering whether to allow unregistered charities already listed on the site to remain there.
A member of the public recently complained that one name on the site was not a charity. It turned out to be one, but was unregistered. This led Bmycharity to ask the Charity Commission for guidance.
Bmycharity's experience prompted Third Sector to look at other sites. It found that some unregistered charities listed on JustGiving showed their Gift Aid numbers or CASC numbers in the space marked "registered charity number".
Sally Chambers, charity marketing manager at JustGiving, said the website provided guidance on its criteria for charities and took the greatest care in validating the data members provided. "The way we describe organisations, such as CASCs or other HMRC-accredited organisations, could be improved," she said. "I will look into the best way of doing this."
Asked about JustGiving's practice, a Charity Commission spokeswoman said it would contact the website to discuss the problem. The format and terminology used was a matter for the operator of the site, she said, "but an organisation cannot be referred to as a registered charity if it is not registered with the commission".
Louise Richards, director of policy and campaigns at the IoF, said it would be a good idea for fundraising websites to reassure donors by having "broad explanatory guidelines" about registered and exempt charities and Gift Aid registration.
The IoF, which is currently revising its electronic media code, would be willing to explore the possibility of working with sites to develop something along those lines, she added.