Child car seats which are illegal to use in the UK are still available to buy from online marketplaces, a watchdog has warned.
The consumer group said 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.
It said 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 said they had removed the seats from sale.
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.
Which? said they had 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."
EBay confirmed the seats found by Which? were illegal and said it had asked the sellers involved to contact the buyers to organise a return and to pay for the return shipping.
An eBay spokeswoman said: "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."
Amazon said: "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."
AliExpress said: "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.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies