HM Revenue & Customs will continue to accept paper forms for Gift Aid "for the foreseeable future", amid concerns that the timetable to introduce the new online system is too short.
HMRC announced last week that it would introduce its new online system, called Charities Online, in April.
The online system is intended to replace the existing claim forms, but HMRC said last week that it would introduce a new form that will allow charities to submit applications on paper.
But the Charity Tax Group said last week that it was concerned about the implementation timescale and warned that the new form "might end up being cumbersome and impractical, and not a credible option for most charities".
An HMRC spokesman said that it was talking to charities about when it would withdraw the existing paper form. "We will continue to accept the current paper forms for the foreseeable future, and no decision has yet been made on when they will be withdrawn," he said.
"The timescale for introducing the new process is generous and we will accept paper claims even after the new repayment process goes live."
He said there would be "a point after which we will no longer accept the current paper forms. We are talking to a wide range of charities and representative bodies to find out when it would be reasonable to set that date, taking into account the needs of charities and encouraging the move to the new processes."
The Institute of Fundraising is due to meet HMRC next week and said it would call for a consultation with the sector on the length of overlap between the paper system and the new system
Peter Lewis, chief executive of the IoF, said the existing forms should be accepted at least until September and will argue for up to a year’s overlap.
"The move to online Gift Aid claims is welcome and should speed up payments to charities and reduce administration, but some of our members might find the implementation timetable very challenging," he said. "We know how important Gift Aid is to our members and we will continue to try to influence transition plans to make them as easy as possible."
Bill Lewis, a tax specialist at solicitors Bates Wells & Braithwaite, warned that the short implementation period could force some charities to close.
"HMRC must ensure there is a long transition period," he said. "If there are delays to processing Gift Aid claims, charities with cash-flow problems could go under because of bureaucracy."