The message is simple: belt up but don’t light up.

Smokers could argue that, with limited places to enjoy a cigarette, their car is their sanctuary – but what if there are children on the backseat?

A recent amendment to the Children and Families Bill backs the principle of making it an offence to smoke in cars when children are present.

The move could become law as Government sources indicated that MPs will be given a free vote on the issue when it returns to the Commons.

It is welcome news for charities such as the British Lung Foundation which has been leading a coalition of charities and health organisations campaigning to ban smoking in cars with children.

Secondhand smoke can be harmful to a child’s lungs. Every year it results in more than 165,000 new episodes of disease among children; 300,000 primary care consultations; 9,500 hospital admissions and around 40 sudden infant deaths.

Research has also shown that because of the confined space within a car, a single cigarette smoked in a moving car with the window half open exposes a child in the centre of the back seat to around two-thirds as much secondhand smoke as in an average smoke-filled pub.

Levels increase to more than 11 times greater than a smoke-filled pub when the cigarette is smoked in a stationary car with the windows closed.

Children are particularly vulnerable to passive smoke, as they have smaller lungs and their immune systems are less developed, which makes them more susceptible to respiratory and ear infections triggered by smoke.

British Lung Foundation chief executive Dr Penny Woods says: “We are absolutely delighted that the House of Lords has voted in favour of this move towards banning smoking in cars when children are present.

“If enacted, a ban would help protect the nearly half a million children who are exposed to toxic secondhand smoke in a car every week.

“This is an issue that the British Lung Foundation has been campaigning on relentlessly. We now look to the Government to listen to the overwhelming support shown across the House of Lords for a ban and take the necessary steps to protect our children’s health.”

Joanne Nykol, from Public Health in Bradford, says: “I think it’s about protecting children from secondhand smoke because unlike adults, children don’t have the freedom to decide how they travel.

“Children have a significantly higher metabolic and respiratory rate than adults, so exposure to secondhand smoke in travel is a potentially serious problem.

“There have been studies done around children being exposed to secondhand smoke in cars and that identified a risk of persistent wheeze. There are some real health issues.”

Joanne adds: “It is also talking about an increase in the risk of cot death, glue ear and asthma. There is no safe level of exposure to tobacco smoke for children.”

Joanne says while they offer a dedicated service for those who want to stop smoking, those who continue should be mindful of exposing children to secondhand smoke in cars and in the home where, she suggests, they should smoke outside.

“If they want to make the choice to continue to smoke, it is doing that while protecting their loved ones,” says Joanne.

Siobhan Freegard, founder of parenting website Netmums, says: “Many parents will be stunned to learn it isn’t already illegal to smoke with a child in the car. The dangers of passive smoking are very clear and doing it in a confined space like a car only makes the problem worse.

“If an adult chooses to smoke, that’s up to them, but they shouldn’t inflict that choice on a baby or young child, who deserves the healthiest start in life.”

One smoker from Bradford, who wishes to remain anonymous, welcomes the proposed ban. She says: “When my children were born I never smoked around them. I smoked outside and I never smoked in the car, but as they got older I am guilty of smoking in the car.”