Comic Relief has developed Gift Aid software for its own use and is now offering it free to other charities. The software, called Gift Aid Interface Link (GAIL), is designed to act as a link between your own donor database and HMRC's Charities Online system, so it's most useful for charities who make large claims or a large number of claims.

You can download the software, and find full technical information, from the GitHub website:

https://github.com/comicrelief/gail