About 90% of shirts, trousers, dresses, shoes and other garments donated to high street shops end up being exported, mostly to Africa. Ghana is the greatest recipient and calls the trade "obroni wawu" - meaning "white men's dead clothes".
Some 30,000 tonnes of second-hand clothes are exported from the UK to Ghana every year, helping to create a booming £50 million market. More than half now bought in Ghana are cast-offs from Europe and the US.
But according to Osei-Bonsu Safo Kantanka, a historian from Bonwire in the Ashanti region of Ghana, the trade is a disaster. "It is killing our culture," he said. "If there was no obroni wawu, a lot of people would turn to the local type of dress."
He pointed out second-hand clothing was much cheaper than native garments. "Our belief and respect for our own things has faded to a degree that if we are not very careful sometime, somewhere, someday, we will not see some of our own things anymore."
Employment in the textile industry in Ghana has collapsed by 90% in the past 30 years. There used to be 40 textile factories, but now there is only one, Akosombo Textiles, and it is operating at less than one-quarter of its capacity.
"It's quite an urgent situation. We feel like we're on the brink of not being able to carry on," said the company's manager, Steve Dutton, who moved to Africa from Manchester 20 years ago. His business is trying to survive by making ceremonial clothes for special occasions such as funerals and weddings.
He added: "We are talking to the government here now to try and get some assistance and so, if help is there, we've got a chance. If it isn't there, our days are numbered."
Kantanka and Dutton both feature in a television documentary made by the Glasgow-based production company, Firecrest Films. Presented by the Paralympic medallist, Ade Adepitan, it is due to be broadcast on BBC Two tomorrow night.
Shoppers in Britain are reckoned to spend £60 billion a year on new clothes. Sales have been booming as prices have fallen, mainly because the clothes are made using cheap labour in Asia.
To make room in the wardrobe for new dresses and shirts, huge numbers are donated to charity shops. There's even an invented word for it - schwopping - promoted by Marks & Spencer and Oxfam, with the help of actress Joanna Lumley. But because charities can't sell most of the items they get in their shops, they sell them on to recycling companies based in Glasgow, the Midlands and elsewhere. They are exported in bales and bought by wholesalers in Ghana, who distribute them to retailers across the country.
The business has brought benefits, with one trader in the capital, Accra, claiming to have made up to £25,000 a day. There is a huge demand for the clothes, which provoke fights at local markets and have put famous high street brands on the backs of some of the world's poorest people.
But environmental groups warn that ultra-cheap clothes are encouraging "wasteful wardrobe habits" in Scotland. "That colourful top may have travelled thousands of miles to sit unused on your hanger before you take it to the charity shop and they send it on another journey across the planet," said Dr Richard Dixon of Friends of the Earth Scotland.
"Just because many clothing items have become ridiculously cheap doesn't mean it's actually alright to buy things we know we'll probably never wear. Of course, we should take our spare clothes to the charity shop or the jumble sale but we need to try to resist buying the useless fraction of it in the first place."
The Secret Life Of Your Clothes by Firecrest Films is due to be broadcast on BBC2 at 9pm tomorrow.