Lethal children’s car seats are still appearing for sale on online marketplaces a decade after concerns were first raised by trading standards officers and a well-known consumer group.

Which? warned in 2014 the fabric seats were potentially dangerous to children due to safety defects and were illegal to use in the UK following tests by Surrey Trading Standards, which dubbed the products “killers”.

Which? is urging parents not to be tempted into buying cheap seats after it found they are still being sold via online sites including Shein and eBay, both of which said they took safety very seriously.

Regulations state only EU-approved child car seats with R44 or R129 codes can be used in the UK.

Approved seats carry a clear orange label, on which the codes are printed, to indicate they have been put through EU safety testing and can therefore be legally sold on the UK market.

In 2014, Surrey Trading Standards tested a fabric seat which fell to pieces in a 30 mph accident. The crash test dummy of a three-year-old child was flung through the windscreen when the straps securing the seat failed.

Which? said families struggling with living costs could be tempted by the cheaper products, which cost as little as £12.50, compared to the more expensive ones that retail in excess of £80.

Stuart Howarth, a car seat safety advisor at Good Egg Safety, which campaigns on child safety, told BBC News he had seen a child using an unsafe seat that had “no support to the body” and “no way of securing it to the car safely”.

“It’s just a lethal piece of material,” he said.

“You might as well just sit on a settee cushion and hope for the best.”

Which? said it found more than a dozen listings of illegal car seats on websites such as eBay, Little Dreams, ManoMano, Shein and Wish.

One listing for a child’s car seat on eBay warned against using it in cars despite the product being described as suitable.

The description in the listing read: “It is best not to use it on high-speed cars.

“We recommend that it be used in non-motorized products such as electric vehicles, two-wheelers… Because it is not a child safety seat that complies with traffic.”

In response, eBay said consumer safety “is a top priority”.

“eBay swiftly removed the listings reported by Which? and the BBC and notified buyers,” a spokesperson said

“We have updated our existing measures accordingly and remain committed to preventing unsafe products from appearing on the site.”

Which? said stricter rules were needed to “impose a clear and robust duty on online marketplaces to prevent the sale of unsafe products” and called for “strong penalties and rigorous enforcement”.

Sue Davies, Which? head of consumer protection policy, said: “It is appalling that these deadly car seats are reappearing on online marketplaces more than a decade after Which? first exposed them, but it is not surprising.”

She said children’s lives “will be at risk” until online retailers were forced to comply with product safety regulations.

Which? advised families to look for retailers who can provide guidance and help fit the seat.

It suggested car seats should not be bought secondhand, as they might have been involved in an accident and damage to the seat may be unclear.

Janis James, chief executive of Good Egg Safety, urged parents not to “skimp” on cash when purchasing car seats for children.

In a statement, Shein said it was committed to “offering safe and reliable products to its customers”.

The online retail giant said the product Which? found listed on its website had been “mislabelled” by a third-party seller and Shein had “taken action against the seller” after removing it from its platform.

It said vendors were required to comply with the company’s rules and “stringent safety standards and must also abide by the relevant laws and regulations of the markets where we operate”.

Little Dreams also told the BBC product safety was a “top priority”.

ManoMano said its online marketplace was used by third party sellers to sell their own products.

It added: “We rely on our sellers to provide a resolution to any product/fulfilment issues.”