Two official investigations are being opened into alarming leaks of poison into commercial airliners in flight. They follow scientific research showing that fumes have rendered pilots incapable of flying their aircraft safely and have put hundreds of thousands of British passengers at risk.

The House of Lords Select Committee on Science and Technology is about to examine the threat as part of an investigation into air travel and health. And the Civil Aviation Authority (CAA) told The Independent on Sunday that the Government is to fit equipment in at least one plane in the hope of studying a leak when it takes place.

Next week a new pressure group, the Aerotoxic Association, will be launched to campaign on the issue – and will start by publishing the Aviation Contaminated Air Reference Manual, which includes details of more than 1,050 incidents in Britain alone.

Air travel has been made possible over the past 60 years by a technique called “bleed air pressurisation”, which takes hot air out of the engine, cools it down and then feeds it – without first filtering it – into the plane’s cabin and cockpit.

Sometimes, however, this becomes contaminated with engine oils containing many different chemicals, which are wafted into the plane to be inhaled by passengers and crew alike. Campaigners are particularly concerned about a neurotoxin called tricresyl phosphate (TCP).

No one knows how frequently an event of this kind takes place because no commercial airliners are fitted with monitors to detect it. But Professor Chris van Netten, an expert on the problem at the University of British Columbia, said he found TCP in every aircraft he examined.

A survey by the British Airline Pilots Association found that less than 4 per cent of contaminated air incidents experienced by its members were reported to the CAA. Sarah Mackenzie Ross, a consultant clinical neuropsychologist and chartered clinical psychologist at University College London, estimated in a recently published paper that on that basis 197,000 passengers on nearly 2,000 UK flights were exposed in 2004 alone.

She has also examined 27 affected pilots for another official investigation being conducted by the Committee on Toxicity, which advises government departments.

She found that all but one of the pilots suffered “chronic health problems, including fatigue, sleep difficulties, fluctuating gastrointestinal problems, numbness and tingling in fingers and toes, memory loss and word-finding difficulties”.

Some, she added, reported “alarming cognitive failures”, including: “being unable to retain, or confusing, numerical data and information provided by air traffic control regarding altitude and speed; completing tasks in the incorrect sequence; setting the wrong cleared level for the aircraft to climb or descend; and being unable to recall important matters such as whether the undercarriage has been raised or lowered.”

Some have had to stop flying altogether, including Tristan Loraine, who is publishing a novel based on his experiences next week. A superfit pilot with 20 years’ experience, he competed in the Ironman Triathlon in August 2005, but had become so ill within a year that he was grounded.

He says the fumes made him feel as if “I had been hit across the head with a baseball bat”; even a trip to Paris as a passenger last Wednesday made him ill again.

“This shows how quickly your life can be turned round, what the exposure can do to you even if you are really fit,” he says.

The CAA says that leaks are decreasing, and that the onboard test – to be run by the Department of Transport – will start “very shortly”. But campaigners are sceptical of both official inquiries and aim to step up the pressure on ministers.