HM Revenue & Customs has drawn up a new Gift Aid declaration for one-off donations, which charities and community amateur sports clubs must begin using by April next year.
The revised wording, which is designed to be simpler and to increase take up of Gift Aid on donations, includes a new line warning people that if they pay less tax in a year than the amount of Gift Aid claimed on all of their donations it is their responsibility to pay the difference.
The shorter declaration for one-off donations removes references to VAT and council tax and includes the words "Boost your donation by 25p of Gift Aid for every £1 you donate" in bold text at the top.
Charity bodies welcomed the simplified text but expressed concern about the new warning.
Andrew O’Brien, head of policy at the Charity Finance Group, said he was concerned that the benefits of the simplified wording might be outweighed by the warning about donors having to pay for any shortfall.
"Research for HMRC found that serious deterrent messages put off eligible donors and didn’t significantly deter ineligible claimants," he said. "We are concerned that the addition of this statement might be counter-productive and see fewer eligible Gift Aid claims made."
O’Brien said that the new declaration would need to be communicated effectively, particularly to small charities so they could plan for the printing of new declaration forms.
The Charity Tax Group warned that the new warning could have a "chilling effect on some donors" but said it recognised the importance of Gift Aid being operated correctly.
John Hemming, chair of the CTG, said: "The introduction of a shorter Gift Aid declaration is a welcome development that should help to ensure Gift Aid is easier to understand for donors, maximising take-up by those eligible for the scheme."
But he said more should be done to promote awareness of the change to ensure that charities did not face the prospect of invalid claims.
"We will also continue to work with officials to ensure that the Gift Aid declaration is as flexible as possible for use on digital platforms, including SMS, where take-up is still too low," he said.
HMRC said charities should begin using the new wording, which applies only to new donations, as soon as possible and by 5 April 2016 at the latest.