as I pointed out further down the thread, (sorry for shouting but my point seems to have been ignored by some)
NOT ALL SUCH DEVICES ARE ILLEGAL, AND THERE IS AN EXCEPTION MADE IN LAW FOR THOSE WHO HAVE LITTLE OR NO COMPREHENSION
I would hazard a guess that a baby would count as a person with little or no comprehension.
At the end fo the day, this is about finding the safest way to travel, keeping a child who does not understand "no" (and some chldren do not understand it until WAY past 15 months old, and some not at all) safely restrained in the car.
Please do take a look at Crelling if you are havingi ssues with this.
they have a range of harnesses and straps, for all types of vehicles.
they are very nice to talk to on the phone, and can advise on various methods.
I have to use an extra harness with dd1, as she will not stay in her seat (she is 5, and uses a high back booster with seat belt). In the event of a crash, the extra harness I use will without doubt cause her some injuries (extra bruising, maybe a cracked rib or two from the buckle), but the fact remains that it keeps her safe in her booster, which will help minimise any other injuries.
without the extra harness, she would not be sitting correctly at all, and would sustain more serious injuries as a result of this.
total no-brainer, imo.