The initiative, to be launched in April 2004, allows people who have completed a self-assessment tax return and have paid too much tax to donate part or all of their rebate to a charity of their choice. However, charities must be registered in order to benefit.
The Inland Revenue has written to the 77,000 charities already registered for Gift Aid telling them about the scheme, but only 20,000 of these have registered for the rebate initiative so far - even though the deadline for applications is 30 September.
"It's a great initiative for charities, especially because the Inland Revenue estimates that it rebated around £3bn last year," said Glenys Weymer, supporter services manager at NSPCC, which has registered for the scheme.
Taxpayers will be told about the scheme in the notes accompanying their tax return, and the Inland Revenue will publicise it more widely closer to the launch next year. Charities are also encouraged to tell their supporters about the scheme.
"Anything that makes people think about charities and giving is excellent, particularly as it relates to tax money that they were not expecting to get back," said Lesley Warner, spokeswoman for Amnesty International.
When the initiative goes live, a list of participating charities will be published alongside their unique identification codes on the Inland Revenue website. Donors are then able to enter the code for their chosen charity on their tax return form.
The forms also include a Gift Aid declaration, and Gift Aid will be paid without the charity having to make a claim. Donations will be made directly into the charity's bank account.
"It looks like a really good idea, and there don't seem to be any extra costs for charities," said Ian Burch, senior accountant in marketing and communication at Barnardo's.
For more information, contact the Inland Revenue charity helpline 0845 3020203.