Retailers who install child car seats are "potentially putting children at risk" by making mistakes, a new report suggests.
An investigation by Which? found that 90% of stores it visited failed to fit car seats correctly, with Babies R Us and Mamas & Papas among the worst offenders.
The consumer group asked staff to fit two different car seats in 42 stores across the UK, but just four managed to fit both correctly and 13 failed to ask essential questions beforehand.
The failings included fitting the seat with the support leg still folded under the base of the seat making it unstable, while one seat was not attached to the car securely enough as the fitter did not know how to install it using the seat belt.
The consumer group said parents should be able to trust the advice they receive, describing the findings as "unacceptable".
Babies R Us and Mamas & Papas both said they would improve training for safety fittings to improve the "disappointing" findings.