The number of deaths and illnesses caused by carbon monoxide poisoning could be much higher than official data from the Health & Safety Executive suggests, says the Gas Safety Trust.

Health & Safety Executive (HSE) figures show four deaths and 117 illnesses caused by CO poisoning in the home in the year ending June 2010, but research by the Gas Safety Trust suggests this is a massive understatement.

In a pilot study, ambulance crews in London carried five carbon monoxide testing kits over the course of a year. They found 83 people had suffered from poisoning in London alone - nearly as much as was recorded for the whole of the UK in the 2008/09 year.

Paramedic Andy Humber, who helped to co-ordinate the pilot, said: "We were shocked by the numbers. We used two types of testing devices, one used on the pulse and one to test levels of carbon monoxide in the breath."

Further studies are being carried out in Leeds, Manchester and Birmingham, and the charity said that if similar results were seen around the country then the official data would "skyrocket".

The Trust said it believed that CO cases were not being picked up because UK pathologists do not carry out routine checks for poisoning after death.

"Overseas research suggests the gaps in our knowledge could be masking significant numbers of CO poisoning incidents," it said in a statement.

Sean Keleher, quality and training manager at Alpha Heating Innovation, said the report highlighted "a worrying lack of awareness".

"There is the possibility that end users are not servicing their appliances regularly due to the worry of increased costs," he explained, "but installers really need to ensure their customers are fully up to speed on the reality of CO poisoning and the steps they can take to reduce the risk.

"The industry has a duty to really hammer home the seriousness of CO - the figures from The Gas Safety Trust demonstrate that we've still got a way to go."