ECE R44.03 and R44.04
Child restraints (baby seats, child seats, booster seats and booster cushions) sold in the UK must conform to the United Nations ECE Regulation R44.03 or later version of the standard.
ISOFIX stands for "International Standards Organisation FIX". It is a new standard for installing child seats into cars, which is being adopted by vehicle manufacturers and is intended to make fitting child seats quick and simple.
Although new child restraints must conform to R44.03 or later version of the standard, people who have child restraints that conform to a British Standard or to an earlier version of R44, may continue to use them.