An Air Canada flight from Toronto to London had to make an emergency landing in Ireland after the co-pilot suffered an apparent nervous breakdown.

Passengers on board the flight to Heathrow said he had to be forcibly removed from the flight deck by fellow crew members in the interests of the plane's safety and yelled that he wanted to "talk to God" as he was restrained.

One of the passengers, Sean Finucane, told the Canadian Broadcasting Corporation he saw the co-pilot being carried into the cabin in restraints 15 minutes before the aircraft descended.

"He was very, very distraught. He was yelling loudly at times. His voice was clear so he didn't sound drunk or anything. He was swearing and asking for God and very distressed. He basically said he wanted to talk to God."

The wife of the Air Canada co-pilot, who has not been named, was understood to be comforting him last night in a psychiatric hospital in Ireland.

Air Canada yesterday said the pilot landed the Boeing 767 aircraft at Shannon Airport shortly before 7.30am on Monday after a crew member became ill and a medical emergency was declared.

The 146 passengers onboard were put up in hotels before departing on another flight that reached Heathrow about eight hours later than scheduled.

The airline yesterday said an investigation into the disturbance was under way. Air Canada spokesman John Reber said the co-pilot was met by medical personnel on landing and a second pilot had accompanied the man's wife to be by his side in a hospital in Ennis, County Clare.

Mr Reber said: "It would be inappropriate for us to specify the cause of the illness, whether physical or psychological.

"The captain and crew followed correct operational procedures when the co-pilot fell ill. At the time nobody's safety was compromised."

Mr Reber added: "He is in the care of health professionals who will determine the extent of his illness. As a matter of course there are always internal reports of any irregularities in an operation. They are always followed up and, if necessary, the appropriate authorities get involved."

Captain Andy Wilson, president of the Air Canada Pilots Association, commended the crew of Flight 848 for its effective handling of the illness of a crew member and safely diverting the aircraft to Shannon.

He added: "Although the illness of flight crew is rare, pilots are fully trained for such an event. The safe diversion was the result of the pilot following standard operating procedures in the professional manner that is expected of Air Canada pilots."

Transport Canada spokeswoman Lucie Vignola said that it will be interviewing the Air Canada flight crew and the airline.