If there's a child in the car, then yes. Otherwise? No. Adults can make informed decisions about whether they want to smoke in their cars or not.
This country is turning into a nanny-state! Obviously it's banned in pubs and clubs now (I actually preferred the smokey smell in clubs to the current smell of stale alcohol, toilets, vomit and sweat.. But that's another story), people are trying to ban smoking *outside* in the street, now smoking in cars.. People will then turn to smoking in their own homes only, where the children are!! I'd much rather see a person smoking in the street, or alone in their car, than in their living room with their children playing nearby as there's nowhere else to go. Banning smoking altogether won't help as 1) A lot of money goes back into the system (ie NHS) through the sale (and extortionate prices) of cigarettes, and 2) If it was made illegal, it would just be gone illegally instead.. A marked increase in crime, and dangerously-made cigarettes, so more hospital admissions due to inhalation of unknown substances (as it wont be regulated anymore) and less money to help fund the treatment.