A British Airways co-pilot who believed he had been poisoned by contaminated cockpit air died from an unintentional overdose of sedatives, a coroner has ruled.

Richard Westgate, 43, died in 2012 after moving to the Netherlands to seek help from a specialist clinic for his symptoms which he thought were caused by "aerotoxic syndrome", which has been called "pilot's disease".

His family said he had been in "excruciating pain" as he suffered from various symptoms, including digestive problems, fatigue, general pain, headaches, loss of cognitive ability, clumsiness and inability to sense temperature.

Mr Westgate, from Marlborough, Wiltshire, died at the Bastion Hotel in Bussum, Netherlands, in December 2012 while undergoing treatment.

Coroner Dr Simon Fox QC recorded a conclusion of accidental death following a week-long inquest in Salisbury.

He said: "Mr Westgate died in his sleep in his hotel room on the night of December 11 and 12 2012 as a result of taking an unintentional overdose of the sedative pentobarbital."

The inquest heard that Mr Westgate had been suffering from a nervous system problem which could have caused his symptoms.

Neuropathologist Dr Daniel du Plessis said a narrowing of the arteries and lymphocytic myocarditis - an inflammation of the heart muscle - might have "quickened" his death.

Mr Westgate believed he had been poisoned by contaminated cockpit air and was suffering from "aerotoxic syndrome".

But Dr du Plessis said he found evidence that Mr Westgate had been suffering from neuritis - inflammation of the nerve roots - which could explain many of these symptoms, including pain, tingling sensations, numbness and balance problems.

Dr du Plessis said organophosphate poisoning - the supposed cause of aerotoxic syndrome - could cause nerve problems but not the nerve inflammation suffered by Mr Westgate.

He added that a more likely explanation for Mr Westgate's condition was an autoimmune condition such as Sjogren's syndrome, which causes the immune system to start attacking healthy cells and tissues.

At the start of the week-long inquest, the coroner ruled that aerotoxic syndrome would not be treated as a factor in Mr Westgate's death.

His death was initially examined by retired Dorset coroner Sheriff Payne, who in February 2015 issued a report raising concerns that more people could die unless action was taken.

He sent his Regulation 28 report to the chief executive of British Airways and the chief operating officer of the Civil Aviation Authority, both of which were represented at the inquest, as well as the Chief Coroner.

It states: "In my opinion, urgent action should be taken to prevent future deaths and I believe your organisation has the power to take such action."

Mr Payne listed the matters of concern, which included "occupants of aircraft cabins are exposed to organophosphate compounds with consequential damage to their death".

He added: "That impairment to the health of those controlling aircraft may lead to the death of occupants. There is no real-time monitoring to detect such components in cabin air.

"That no account is taken of genetic variation in the human species such as would render individuals tolerant or intolerant of the exposure."

Lobby group Global Cabin Air Quality Executive is campaigning for equipment to be installed in aircraft to monitor air quality, which is supported by unions representing some airline workers.

Their research suggests that this air, known as "bleed air", can become contaminated with engine oils and hydraulic fluids leading to illness among cabin crew through repeated exposure.

In 2015, the Unite union launched a helpline and revealed 17 personal injury claims had been made involving former and current cabin crew staff working for UK airlines.

But the industry insists that incidents of smoke or fumes on planes are rare and there is no evidence of long-term health effects.

Speaking after the inquest, Mr Westgate's mother, Judy, read a statement on behalf of her family.

"Richard loved life and had so much to live for. He found his calling as a pilot, both in paragliding and flying passenger jets, something he considered a privilege," she said.

"A few years ago he started to get sick but his symptoms baffled doctors; either they didn't know what was wrong or they chose not to help. The result was they all turned him away.

"His sickness turned to excruciating pain - and still he felt the doctors betrayed him.

"When Richard died four years ago, Coroner Sheriff Payne believed there could be a problem with poisons in cabin air of the aircraft Richard flew and started the inquest accordingly.

"To our dismay, however, the coroner was suddenly switched last year and the new coroner instructed that aerotoxic syndrome would not be discussed as a 'proper issue' in relation to Richard's cause of death.

"The inquest has ruled he ultimately died of an accidental overdose of a sedative - a sleeping tablet - but the real questions are: What made him so sick in the first place? And do the airline industry have something to hide?

"My son suffered so much and our only peace of mind is to believe it was not all in vain, as his body has revealed some vital clues to help find the truth.

"The results of Richard's post-mortem showed he had damage to his nervous system and heart. The organophosphate toxins in cabin air have been shown to cause this kind of damage, leading to many of the same symptoms and pain that my son experience.

"The court has heard that repeated doses of poison can also cause nerve damage, at exposure levels previously thought safe to humans.

"Medical experts have said that organophosphates cannot be ruled out in causing his condition, so the questions therefore remain.

"Further discussion and questions about this was not allowed by the coroner.

"We know there are more sick passengers and crew and we hope today will encourage the millions who fly to ask questions to ensure more is done to make sure others don't suffer like my son.

"We would like to thank Richard's friends and work colleagues for the messages of support and stories of his life.

"He was a wonderful son, friend, brother, uncle and godfather who just happened to be susceptible to breathing toxic air.

"One day the truth will out."

Mrs Westgate said she found it frustrating that the airline industry was denying responsibility for the problem.

"The airlines cannot categorically say that air in these aircraft is safe," she said.

"They refuse to monitor and test for toxins, so of course they have no evidence because they will not look for it.

"The longer they deny there is a problem, the harder and more costly it's going to be when they are proved wrong.

"Just like the tobacco industry in the 50s refusing to admit smoking causes cancer, the airline industry has its head in the sand.

"The inconvenient truth for the airlines is that low doses of toxins in cabin air, over hundreds of hours, can hurt people.

"The airline industry should be ashamed of itself. My son suffered so much unnecessarily and they have done nothing to protect people.

"The longer you leave it, the harder it is going to be, so we just expect those responsible to do the right thing."