More than half of the British population are at risk of carbon monoxide poisoning because they do not have an alarm in their home to detect the potentially fatal gas, according to new research.
The study, conducted by the Carbon Monoxide - Be Alarmed! campaign in August this year, found 35 million Britons to be at risk - 31 million in England, 2.4 million in Scotland and 1.6 million in Wales.
These findings have been published the day before the installation of carbon monoxide alarms becomes compulsory in Scotland when a fuel-burning appliance is fitted.
Lending their support to the campaign are Catherine McFerran and Katrina Davidson from Newtownabbey in Northern Ireland who lost their 18-year-old sons, Neil and Aaron respectively, in 2010 to carbon monoxide poisoning while staying at a holiday apartment.
"Since our sons were cruelly taken from us by this silent killer, we have campaigned to try to prevent similar tragedies, they said in a joint statement.
"Carbon monoxide alarms are now compulsory for all new homes in Northern Ireland and when new appliances are installed in Scotland, but many people in older homes or in the rest of the UK may still be at risk.
"Make sure you and your loved ones are protected, make sure you have a working, audible carbon monoxide alarm in your home. It is not a risk worth taking."
Carbon monoxide is known as a silent killer because it has no smell, colour or taste and can be produced by a faulty or poorly ventilated fuel-burning appliance such as a boiler, fire or cooker.
An alarm that makes a sound when the gas is detected is the only way to ensure protection, the Carbon Monoxide - Be Alarmed! campaign group have said.
Dr Rob Hicks, GP and medical commentator, said: "At high levels, carbon monoxide can kill you in a matter of minutes. At lower levels, it can cause a range of serious and long-term health problems.
"The symptoms of carbon monoxide poisoning are very hard to recognise, even for doctors, as they are similar to many common illnesses like flu and food poisoning.
"This makes it very easy to miss the warning signs, with life-threatening consequences. Don't take the risk. Most people wouldn't dream of not having a smoke alarm - it should be the same with carbon monoxide alarms."
The research published today also revealed some confusion.
Some 44% of the people without a carbon monoxide alarm said they did not have one because they have a smoke alarm. Researchers say this suggests these people do not realise that a smoke alarm does not detect carbon monoxide.
The results also showed that the number of people who said they had a carbon monoxide alarm (43%) was higher than the number of homes found to have one or more during service visits.
The research was carried out by ICM research in August 2013 and involved 10,604 Britons across England (9,251), Scotland (849) and Wales (504).
Derek Mackay, Scottish Government minister for planning, said: "We are aware that more can be done to encourage installation of carbon monoxide alarms in homes with existing fuel-burning appliances.
"It is important that people protect themselves from the deadly risk of carbon monoxide poisoning and campaigns such as 'Carbon Monoxide - Be Alarmed!' are vital in raising awareness of this.
"This is why we are working with them to adapt their advice leaflet for use in Scotland. Thereafter we intend to work with other bodies to make the leaflet widely available, raising awareness of the benefits that alarms can bring."