A council has advised people against using doorstep charity collection bags and to donate unwanted clothes directly to charity shops.
Trafford Council in Greater Manchester issued the warning after reports of bogus charities issuing sacks and incidents of genuine bags being stolen.
It said criminal gangs had driven round streets in advance of legitimate collectors and taken sacks.
Campaign group Charitybags claimed clothes were often sold abroad.
Trafford Council also advised people that if they use the bags they should ensure there is a registered charity number printed on them and to check the number on the Charity Commission website.
The Charitybags website states that charity bag scams deprive legitimate charities of up to £10m a year and that stolen second-hand clothes were frequently sold in Easter Europe or Africa.
Executive councillor John Reilly said: "People recycling their unwanted goods in aid of a good cause are doing the right thing and it is something we would really encourage.
"The best way to ensure that deserving causes get the most benefit is to follow a few simple steps to check things out, that way we can keep the profits from recycled goods out of the hands of conmen and fraudsters."
A Cancer Research UK spokesman said: "Cancer Research UK does not carry out any commercial partnerships to collect stock from people's homes.
"Anyone particularly concerned can also bring their donation directly to one of Cancer Research UK's 600 shops around the UK, where 100% of profits from selling donated items funds our life-saving work.
"Our shops are desperately short of stock, we need people to continue to donate good quality clothes and home ware to raise funds to help support our work to beat cancer."