Smokers who light up in vehicles with children inside will face fines in England and Wales as anti-smoking measures are expanded to protect young people from the dangers of second-hand smoke.
The ban went into effect Thursday but police are not expected to issue a rash of fines as the public becomes accustomed to the regulation.
The National Police Chiefs' Council said in a statement that police would take an "educational, advisory and non-confrontational approach" for at least the first three months of the ban.
"This would see people being given warnings rather than being issued with fines," police said.
Smoking advocates called the new law unenforceable, but health officials and anti-smoking groups hailed the measure as the most important since a general ban on smoking in workplaces and enclosed public spaces took effect in England in 2007.