MSPs who passed legislation to ban smoking in cars that are carrying children were told that the only similar legal intervention resulted a ten per cent cut in the proportion of youngsters exposed to secondhand smoke.

Holyrood politicians voted unanimously for the legislation which will mean fines of up to £100 for anyone who smokes in a car which has a passenger under the age of 18.

It aims to protect children from the harmful effects of second-hand smoke.

The Smoking Prohibition (Children in Motor Vehicles) Bill was introduced by Liberal Democrat MSP Jim Hume.

Some pro-smoking groups and tobacco companies feel that the research shows that relatively few adults smoke in a car with children and that legislation was over-the-top.

In response the pro-smoking group FOREST described the Bill as a “disproportionate response to a relatively rare problem”.

A government briefing paper to MSP that was circulated said: "There is some evidence from Canada that legislative interventions can be effective in reducing children’s exposure to second-hand smoke in vehicles.

"The researchers used Canadian survey data from children aged 10 and over to evaluate whether legislation reduces children’s exposure to second-hand smoke in cars.

"The study found that the legislation reduced the proportion of children exposed to second-hand smoke by around 10 per cent relative to the period before the law was implemented and in provinces that did not adopt such laws."

But a summary of the consultation responses shows that 84 per cent of all respondents supported the proposed Bill. The main reason for supporting the proposal was to protect the health of a vulnerable section of society like children.

A law banning smoking in vehicles carrying children has come into force in England and Wales in October. Drivers and passengers who break the law could face a penalty fine of £50 - but police say they will take a non-confrontational approach initially.

Other countries, including Australia, several US states and territories, have also implemented bans on smoking in cars with children present.

The briefing document said that the anti-smoking charity Ash Scotland inferred from surveys that it is likely that at least five per cent of young teenagers in Scotland are in vehicles where smoking occurs.

A 2013 UK study found that the average concentration of secondhand smoke in a car was around one-third of that found in Scottish pubs prior to smoke-free legislation and around three times World Health Organisation air quality guidelines.

Public health minister Maureen Watt said after the legislation was given the nod that it would contribute to the Scottish government's drive to cut the number of children exposed to second-hand smoke from 12 per cent to six per cent by 2020.

And she said that Scotland had shown itself to be a "world leader on tobacco control".