Police chiefs have raised fears that officers could be diverted away from work tackling terrorism and organised crime to enforce a proposed ban on smoking in cars where children are present.

Liberal Democrat MSP Jim Hume wants smokers to be fined £100 if they are caught lighting up in a vehicle when under-18s are present.

But Police Scotland and others have voiced concerns about the impact it could have on the force if his member's Bill - which has already won the backing of the Scottish Government - is passed.

Assistant Chief Constable Bernard Higgins and Chief Superintendent Iain Murray will raise the issue when they give evidence on the Smoking Prohibition (Children in Motor Vehicles) (Scotland) Bill to Holyrood's Health Committee.

In a submission to MSPs ahead of tomorrow's meeting, Police Scotland said it would be the "sole enforcement authority" for the legislation, suggesting this needs to be "carefully considered".

The force said it backed the Bill "as a means of addressing the public health issue presented by smoking in vehicles in the presence of children", but questioned whether police officers should be the only ones to enforce it.

"As a public health issue is it proportionate or necessary to justify the use of limited police resources to enforce it?" the submission from the police said.

"The proposed legislation will only have an impact on public health and, whilst commendable, does not sit comfortably within the Police Scotland policing plan and the force priorities.

"Police Scotland would, therefore, question the use of police resources to enforce this legislation and their diversion from work focusing on the force priorities such as organised crime and counter terrorism, for example.

"The work of road policing officers in particular is focused on reducing road casualties and tackling road crime, and whilst this is a broad remit there is little, if any, room for matters of public health."

Police Scotland has suggested councils could also have a role in enforcing the ban, if it is brought in, arguing local authority officers could do this around schools when children are being dropped off and collected.

"In summary, Police Scotland would contend that the potential impact on the police, as the sole enforcement authority, may be more than that first envisioned by the Bill," the force said.

"The police have enough on their hands already without having to investigate and possibly prosecute drivers who might be smoking in a car carrying children."

The campaign group Forest, which aims to protect the interests of adults who choose to smoke, also argued: "The police have enough on their hands already without having to investigate and possibly prosecute drivers who might be smoking in a car carrying children."

Its submission to the committee said: "Frankly, so few adults smoke in cars with children these days it will be like looking for a needle in a haystack and a complete waste of police time and money.

"Currently, the overwhelming majority of adult smokers self-regulate when it comes to smoking in cars with children.

"With or without a law they will continue to self regulate, hence we believe legislation is a gross overreaction to a very small problem."

Mr Hume said: "I am delighted to have Police Scotland's support for the aims of my bill.

"It chimes with the significant 85% of Scots who have said they would like to see children protected from second-hand smoke whilst in the confines of a car.

"This will help moves towards the Scottish Government's stated vision for a smoke-free Scotland by 2034.

"In 2013/14 Police Scotland detected over 36,000 seatbelt offences and just over 34,000 mobile phone offences. This demonstrates that detection is perfectly possible."