What are the new rules?
Children under three: until his third birthday, your baby or toddler must use a child car seat appropriate for his weight in any vehicle (including vans and other goods vehicles) regardless of whether he is sitting in the front or the back. If you can't fit a child seat for your baby or toddler then he can't travel legally. In addition, the new rules also say that rear-facing baby seats MUST NOT be used in a seat protected by a frontal air-bag unless the air-bag has been deactivated. If you are using a forward facing child seat, see what your car's handbook says about children in seats with frontal air-bags. The advice can vary from car to car.
Children three and over: until he is 135cm tall (approximately 4ft 5in), your child must use an appropriate car seat. Using an adult seat belt for a child who is under 135cm tall is no longer legal.
Are there any exceptions?
Children under three: there is only one exception to the new law for children under three. If you are travelling in the rear of a taxi and you don't have a car seat with you your baby or toddler can travel without a seatbelt.
Children three and over: there are only three occasions where children over the age of three and under 135cm tall can travel in the back of a car using an adult seat belt. These are:
• In a taxi, if an appropriate child seat is not available.
• For a short distance "in an unexpected necessity". This exception is designed to cover situations where you might have to collect your child, or someone else's, at short notice and don't have the right car seat with you.
• Where you need to carry three children but can only fit two car seats in the back of the car. In this case the third, and preferably tallest, child could use an adult seat belt.
A very few cars, for example classic cars, don't have any seat belts fitted at all. If you are travelling in a car like this, children aged three and over are allowed to travel in the back unrestrained. However, just because it is legal doesn't make it safe.
Hope that helps, bit non commital about air bags & I bet the manufacturer, whicever one, will fudge the issue too