My day job is advising on seat belt use and effectiveness so hopefully the following will assist people to weigh up the risks. It is understandable that people wish their cars to be as safe as possible, and three point seat belts are undoubtedly safer than lap belts - but only if they are installed correctly. There is no shoulder belt upper mounting in the layout shown above. In a severe frontal impact it is likely to compress the spine. In an angled impact, the shoulder might slip out and render the seat belt almost useless. If used correctly, a good lap belt is better than a poor lap/shoulder belt. Lap belts should be adjusted to fit snugly across the pelvis, beneath any thick coats etc. They should not be loose and/or lie across the soft abdominal area. If there is space, it's better to use a retractor seat belt, as it does not have to be manually adjusted. If three point seat belts are installed in a vehicle designed and tested only for lap belts in the rear then, apart from the risk of causing unnecessary injury, if anything did happen the seat belt installer would be at risk of civil liability proceedings. The motor insurers might also take a dim view of the modifications and refuse to underwrite any claim. The legal issues can be avoided by using it as designed i.e. with a lap belt fixed to the anchorages provided. To be fair, serious problems are only likely to occur in a severe collision. But it is not a risk I would take. Regards Steve H