Posted By sagalout Ron, Booster seats and cushions are commonly designed to work with a three point belt and require the diagonal strap to safely restrain an occupant. So, using one with a lap belt is not how they are designed and therefore not safe. There are some about which are crash tested and pass the ECE R44 using just a lap belt. The manufacturer should be able to tell you whether those you use are in that category. I cannot tell you what the injury potential difference between using an incorrect seat cushion with a lap belt or relying upon the adult lap belt would be. I just wouldn't use the seat cushion unless it were designed for use with a lap belt.

Posted By Ron Impey Hi Ken, I already did that on 3/10 and they advised: 'It is safer for a child to sit in an appropriate child restraint rather than just adult belt. However I am not sure that there are any booster cushions that can be used with lapbelts. If you use a child restraint with a lapbelt it must be specifically designed for the purpose. It may be worth ringing manufacturers'. I contacted the top manufacturer who supplied me with a list of their lap belt compatible child seats, etc. However, this did not include any booster cushions. They also advised that: 'Use of a booster on a lap belt would actually be more dangerous for the child. The point of pivot is raised and thus generates much more movement of the head in an accident'. Both I and a road safety officer from my local council are not convinced about this opinion; hence this posting seeking the opinions of others.