Concern about the death toll from carbon monoxide poisoning has prompted the Health and Safety Executive to conduct a major review of the gas industry and the way it is policed.

About 20 million households in the UK use natural gas which, without proper care, could be poisoning customers.

According to official statistics, approximately 30 people die each year from what is known as the "silent killer".

But BBC Scotland's Frontline programme has spoken to experts who believe that, because so many cases go undetected and undiagnosed, the figure could actually be 10 times that.

Council fined

A faulty gas heating system in a council house in Glenrothes killed one man and his girlfriend suffered permanent brain damage.

Fife Council admitted causing the death of Mark Taggerty and causing injury and suffering to Hazel Brown.

The council has since replaced all the defective heating systems in its homes and was fined £5,000 earlier this year for breaching gas safety regulations.

The dead man's family are now suing the local authority.

Poor installation

The natural gas used to fuel water heaters, fires and boilers is not poisonous, but poorly installed or inadequately maintained appliances can give off potentially lethal carbon monoxide.

It can also build up in a room if chimneys, flues and vents are blocked, or if there is not enough fresh air in the room to keep the gas burning properly.

The gas cannot be seen, tasted or smelt, but in sufficient concentrations it can cause death within a matter of hours.

Many gas users are not fully aware of the potential dangers of the appliances around them and in some cases they do not find out until it is too late.