From October 1 2015 it will be illegal to smoke in private vehicles that are carrying a child. From that date, private vehicles will have to be smoke free if they are enclosed, there is more than one person present and one of them is under the age of 18. 

The law is changing to protect young people from second hand smoke - over 80 percent of cigarette smoke is invisible and opening windows does not remove its harmful effect

But new research has revealed that a huge majority of drivers do not believe that the new law will be effectively enforced.

An RAC survey has found that 92 percent of British motorists feel the prospect of effective enforcement, which includes a £50 fine, is unlikely.

Nine out of 10 people questioned knew about the new law, but only 50 percent knew it was coming into force this week. Four in 10 had no idea as to its start date.

RAC spokesman Simon Williams said: "While the motoring public know this new law is coming, our data shows that a significant proportion are not aware just how soon it takes effect.

"It is worrying that nine in 10 motorists have concerns about the extent to which the new law is likely to be enforced. This is perhaps well-founded as traffic police officer numbers have fallen by nearly a quarter (23 percent) between 2010 and 2014 across forces in England and Wales, so it is hard to see how people flouting the law are going to be caught.

"The new ban joins a raft of other laws that have been introduced in recent years such as making it illegal to undertake or hog the middle lane of a motorway. But without sufficient enforcement there is a real danger that these laws will quickly be forgotten by a large proportion of the motoring population."

The legislation covers any private vehicle that is enclosed wholly or partly by a roof. So a convertible car with the roof completely down is exempt from the ban.

A vehicle with the sunroof open is still enclosed, and will be covered by the legislation - as is smoking while sitting in the open doorway of an enclosed vehicle.

The rules apply to motorhomes, campervans and caravans when they are being used as a vehicle but don't apply when they are being used as living accommodation.