I found the following which may help anyone else
The ISOFIX System
With the emphasis on vehicle safety mainly falling on the front seat passengers, child protection used to be somewhat of an after thought. The ISOFIX system, for child seats and restraints goes some way to change this.
The ISOFIX system has been designed to make the car a children safe environment, even if they are not able to use the cars main restraints or seats. The ISOFIX system is a system of anchorage locations fitted to the seats of a vehicle to which a child's seat or booster cushion affixes.
Car manufacturers provide small, cheap and inconspicuous attachment points to the seats of their new vehicles, an ISOFIX seat then attaches to these points with a simple push fitting. These attachments points are in a standard location and use the same fixings in all vehicles, meaning child seats can be removed from one vehicle and fitted to another with the ISOFIX system installed.
The ISOFIX system has two anchorage points at the rear of a standard seat to which a ISOFIX enabled child seat affixes. The seat clips into the ISOFIX mountings, which in turn are securely fixed to the vehicles chassis. This means that once the seat is fixed then it won't move. It also means that you don't have to rely on the cars existing seat belts to secure the seat in position. Most ISOFIX seats have their own belt system for securing your child, be this a laptop or a four/five point harness system.
Because the car seat cushion is not standardised for height, angle and stiffness, seats using two-point ISOFIX have to be tested and approved for use in specific car models. This means they are tested in a specific model of vehicle and not on a universal test sled. This does have a down side that specific models can only be used on specific vehicles.