Shops including Amazon and TK Maxx have been selling faux fur clothes and bags which are actually made from rabbit, fox and raccoon dog fur, a BBC Watchdog Live investigation has found.
Widespread concern over animal cruelty has led to real fur very nearly disappearing from most UK high streets.
Both TK Maxx and Amazon said the products were no longer available.
TK Maxx said it does not knowingly buy real fur and an error was made. It has offered refunds to anyone affected.
Watchdog Live presenter Steph McGovern visited a branch of TK Maxx - which has had a no-fur policy for 15 years - and bought a handbag made from fox fur.
And a pair of shoes purchased on the store's website featured fluffy bobbles which were made from raccoon dog fur.
Meanwhile, two bobble hats sold by Amazon and described as "faux fur" were made with raccoon dog fur.
Rabbit fur was also found in a jumper purchased at an AX Paris outlet store and in fluffy bobbles on a pair of shoes bought from fashion label Missy Empire.
The tests were carried out by textile analysis expert Dr Phil Greaves. He told the programme: "All animal fibres have particular structural features.
"And it's the actual nature and characteristic of these which determines the species of origin.
"These fibres are very distinctive once under the microscope."
The tests came after shopper Chloe Salvi, from Edinburgh, said she was concerned about a bobble hat that she had bought on eBay. It had been described as fake fur.
"As soon as I touched it I felt something wasn't right," she said.
"I've got a cat, and it reminds me of when I cuddle her. It wasn't the way a faux fur pom-pom should feel."
Tests later revealed it had been made from raccoon dog.
"I can't help thinking about what animal this has been taken off, just for me to have a pom-pom on a hat," she said.
eBay does not have a no-fur policy, but the website says it expects sellers to describe products accurately.
The online auction website has asked the seller to amend or remove the listing and apologised for any distress caused to Chloe.
Though fur farming is banned in the UK, it is not illegal to import fur from other countries.
Earlier this year, a committee of MPs recommended a consultation on banning sales of real fur. It said the current labelling of fur products was "not fit for purpose".
Claire Bass, the executive director of Humane Society International in the UK, said she would like to see a change in the law over imports, because of the conditions in which many animals are kept.
She said: "Retailers need to be do more to give consumers the confidence they need to buy fake fur and not be worrying that it might actually be fox, rabbit or mink."
TK Maxx told Watchdog Live: "Our buyers understand that we do not knowingly purchase items containing real fur.
"Despite our robust processes, an error can occasionally occur. As soon as this is brought to our attention we remove the item from sale and review the journey of that product.
"Any customer who has purchased such an item can return it to any TK Maxx store for a full refund with our most sincere apologies."
In response to the investigation, Amazon told Watchdog Live: "All Marketplace sellers must follow our selling guidelines, and those who don't will be subject to action including potential removal of their account.
"The products in question are no longer available."
AX Paris, which has a fur-free policy, said the jumper was in an isolated product line and not branded with AX Paris. It said investigations are ongoing.
Missy Empire, which is also anti-fur, said it was "dismayed" to find its product contained fur and it was no longer available. It apologised to customers and said it is running further checks on other faux fur items.
Watchdog Live is on BBC One on Wednesday 14 November at 20:00 GMT.