The weight of clothing donated to charity through doorstep collections in the UK was 20 per cent lower in the first quarter of this year than in same quarter last year, according to the collections company Clothes Aid.
A spokeswoman for the company blamed the drop on the rise in bogus charities and the theft of collection bags from doorsteps.
Areas particularly affected included Cardiff, where the weight donated in February was 57 per cent down on the same month last year, Newcastle-upon-Tyne, where the fall was 39 per cent, and Medway, where it was 48 per cent.
Michael Lomotey, business manager at Clothes Aid, said: "Every day we receive reports through our helpline about thieves taking donations away from legitimate charities. The proliferation of so-called bogus charities is having a huge impact on our collections this year."
Karen England, director of fundraising at the children's charity Make-A-Wish Foundation, said it had seen a significant reduction in the amount of clothing donated.
In 2009, she said, clothing collections raised £280,000 for the charity. In 2010 they raised £180,000.
"It is having a significant impact on us," she said. "I think a lot of it is fear of bogus collections. The general public have become worried about whether a collection is legitimate and are cautious about putting something out."