Sue Ryder Care was the first charity to start claiming Gift Aid on donations to its shops.
The charity estimates that it now raises £50,000 a week in retail Gift Aid through its 350 stores.
It is able to claim Gift Aid on donated items by selling them on behalf of the donors and then asking them to donate the money raised to the shop.
Julie Beames, business development manager at Sue Ryder Care, says the system is not expensive, but requires investment in technology and training.
"It requires you to give each donor a unique number, attached to everything they donate, and to know when those items are turned into cash and what the value of the goods sold on their behalf is," she says. "You need a system for tracking that data."
Each charity shop is equipped with broadband and a PC, with a standard form available. Details of donors are entered into the system, along with unique ID numbers attached to each item they donate. When donors' goods are sold, they are sent a letter asking them to confirm they are happy for Gift Aid to be claimed.
Beames says the data can be used for other purposes. "We learn a lot about our donors by analysing this data," she says. "And it gives us a list of people who are sympathetic to us. It has also given us a much clearer idea of our stock movements."
The system, she says, is cheap, considering the benefits it brings. "Total costs for us are about 5 per cent of the Gift Aid reclaimed. For small charities, there are now several companies that offer a complete system."