The Health and Safety Executive describes CO as "a colourless, odourless, tasteless, poisonous gas". It is produced when carbon-based fuels, including gas, oil, wood and coal do not burn fully because of a lack of oxygen supply.

When CO enters the body, it prevents the blood from bringing oxygen to cells, tissues and organs. This lack of oxygen causes the body tissues and cells to die.

Carbon monoxide also causes blood vessels in the body to leak, which can lead to swelling in the brain, causing unconsciousness and neurological damage.

Early symptoms of CO poisoning are often mistaken for other ailments such as flu, viral infections or simple tiredness.

The most common symptoms are tiredness, drowsiness, headaches, giddiness, nausea and vomiting.

Sufferers may also experience chest pains, breathlessness, stomach pains, erratic behaviour and visual problems.

Stephanie Trotter of CO-Gas Safety says: "Family members can suffer different symptoms.

"For example, the mother may be tired and have a headache, the son may be dizzy and act strangely, the daughter may have a bad stomach ache and the father may just be bad tempered."

The severity of poisoning depends on the length of your exposure and how much gas you have been exposed to. CO poisoning can cause permanent brain and heart damage as well as death.

If several people in the same building develop flu-like symptoms without a temperature and you think it could be linked to a CO leak, stop using all your cooking and heating appliances, open the windows and doors and call the National Gas Emergency Service Helpline on 0800 111 999.

Visit your GP or Accident & Emergency department urgently and say that you believe your symptoms may be related to carbon monoxide poisoning.

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