Great Ormond Street Hospital Children's Charity has lost £500,000 because of a sharp rise in thefts of donated clothes since January, a new report reveals.
The study estimates thefts of GOSHCC bags have grown from about half a tonne of donated clothes a month in 2004 to 50 tonnes a week in July 2006.
The charity is also facing an estimated £200,000 loss over the next six months because of what it describes as "misleading" collection schemes, according to the study, which predicts that other charities could also be at risk.
Research conducted by Clothes Aid, the company that collects textiles from donors' doorsteps on behalf of GOSHCC, suggests that profit-making organisations use letterbox leaflets to make rival appeals for clothing for what look like charitable purposes in eastern Europe.
The researchers believe that collection times are planned to coincide with GOSHCC collection days to allow these organisations to steal GOSHCC-branded bags and sell the contents.
"When this happens, it is not unusual for a whole day's collection to be stolen in one area," said Michael Lomotey, the report's author and head of collection protection at Clothes Aid. "It is too much of a coincidence that they are always there when we have collections - what we don't know is how they know about our collection dates."
Lomotey predicts that other charities that operate collection schemes could stand to lose between £6m and £7m in the next year if the trend continues.
Both GOSHCC and Clothes Aid are calling for a concerted effort from police, trading standards officers and other charities to help end such schemes, which are threatening to put Clothes Aid out of business.
"When we reported thefts of bags in the past, we felt that little was done," said Lomotey. "We realised we needed to collect data to show how big the problem is."
The Association of Charity Shops agreed that the collection scams were harming charities. "These seem to be incredibly sophisticated operations," said David Moir, head of policy and public affairs at the association.
"We know there is a sizeable market for rag. Prices are high, and there are clear attractions for thieves."
Clothes Aid now plans to use the report to lobby chief police officers, the Crown Prosecution Service and other agencies to take action.
The Charity Commission has warned charities to beware of a scam involving cheque donations.
Fraudsters give a cheque to a charity and later request that up to half the money is repaid. The original cheque bounces, leaving charities that have made a repayment out of pocket.
David Locke, head of charity services at the Charity Commission, warned: "Charities should treat these requests with extreme caution."