AMAZON, eBay and AliExpress have been selling car seats that are illegal to use in the UK, a watchdog has warned.
The seats, made of fabric, offer "almost no protection" in the event of a car crash and sell for as little as £8, Which? found.
The consumer group says the seats clearly lacked the support needed to protect babies and toddlers despite being described in listings as suitable for newborns and children up to the age of five.
Which? adds that online marketplaces should have been able to recognise them as inadequate and remove them from sale as soon as they were listed in order to prevent customers from buying a product that puts their child at risk.
Amazon, eBay and AliExpress all say they've since removed the seats from sale.
The danger was first highlighted in 2014 after Surrey Trading Standards and manufacturer Britax carried out a 30mph crash test which resulted in a fabric seat falling to pieces.
The crash test dummy of a three-year-old child was flung through the windscreen when the straps securing the seat failed.
At the time, Surrey Trading Standards dubbed them "killer car seats" and removed dozens of them from sale.
But Which? says they have repeatedly re-appeared for sale on online marketplaces ever since.
Regulations state that only EU-approved child car seats can be used in the UK.
Approved seats carry a clear orange label with the codes ECE R44-03, ECE R44-04 or ECE R129 to indicate they have been put through EU safety testing and can therefore be legally sold on the UK market.
Which? recently claimed that the UK's consumer enforcement system is on the brink of collapse, suggesting that reforms must include measures that improve monitoring and policing of online marketplaces.
Alex Neill, managing director of Which? home products, said: "Parents will be horrified at the thought they could be unwittingly putting their child's life at risk with one of these 'killer' car seats.
"Online marketplaces cannot continue to turn a blind eye to dangerous and illegal products being sold on their sites.
"The UK's product safety regime is in dire need of reform.
"More needs to be done by big businesses and Government to protect consumers from dangerous products."
Can I get a refund on my car seat?
HERE'S what AliExpress, Amazon and eBay told The Sun when we asked whether customers with these car seats can return them:
AliExpress: The online retailer says third-party sellers on its website have to give buyers the right to return items if they're not as described or of low quality - but they have to do this within 15 days of purchase and it isn't extending the time limit for shoppers who bought the car seats. Under EU rules, buyers have a right to a refund or replacement where an item is faulty, but this is only if the seller is also in the UK or EU. AliExpress is a Chinese firm so it's unlikely shoppers will have this protection.
Amazon: The online retailer says all affected customers have been contacted but it hasn't told us whether they've been offered refunds or replacements.
eBay: The auction website says it has asked the sellers involved to contact buyers to organise a return and refund, and to pay for the return shipping.
Amazon told The Sun: "All 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."
Meanwhile, AliExpress told us: "AliExpress considers the safety of all our customers, especially children, to be of paramount importance.
"After we were told by Which? about these third-party listings, we took prompt action to remove them.
"We will continue to take action against sellers who violate our terms of use."
An eBay spokesperson told The Sun: "The safety of our customers is paramount and we do not tolerate the listing of non-compliant items by sellers.
"Our specialist teams work with regulators and Trading Standards to ensure our block filters stay up to date, using sophisticated software that monitors billions of listings a day to remove any prohibited items."
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