Volkswagen and Seat are selling vehicles which the Volkswagen Group knows have faulty seat belts, a consumer group has claimed.
When all three rear seat belts are in use in affected cars driven at high speed, the rear left passenger side can become unbuckled.
After the fault was discovered in May by Finnish motoring magazine Tekniikan Maailma, Volkswagen Group recalled thousands of new VW Polos and thousands more Seat Ibizas and Seat Aronas.
It is not the first time this year a vehicle manufacturer has had to recall its product as BMW recalled 312,000 UK models at risk of electrical issues earlier this year.
But consumer group Which? described the procedure of securing the central and rear left buckles together as a "temporary measure".
It found that the affected cars were still being sold "without a permanent fix in place", with a warning sticker being placed on dashboards.
Alex Neill, Which? managing director of home products and services, said: "It’s shocking that VW and Seat are selling thousands of cars that they know have a serious safety issue but don’t yet have a proper fix for.
"Volkswagen Group should not be selling these potentially dangerous vehicles at all.
"Supplying a warning sticker is a startlingly inadequate response to a fault which is putting lives at risk.
"The DVSA [Driver and Vehicle Standards Agency] must be given the powers it needs to hold manufacturers to account."
A spokesman for Volkswagen Group insisted the vehicles affected by the seat belt fault had been approved for sale and were safe to drive.
He said customers were being advised not to use the middle seat until they have had the buckle modified.
A "permanent solution" was due to be available from November.
The spokesman added: "We have asked retailers to ensure that all prospective purchasers of affected new or used vehicles are made aware of the current guidance not to use the middle rear seat."
DVSA’s head of national enforcement Caroline Hicks said: "DVSA is in discussion with VW Group over the seatbelt defect and a full recall will be made when a suitable fix is agreed."