Judith Haig described how she tried in vain to hold on to her friend and business partner, Charles Bruce, when he unbuckled his seatbelt and opened the door of their Cessna 172 Skyhawk as they flew over Oxfordshire on January 8.

As Ms Haig grasped the waistband of his trousers with one hand and tried to control the aircraft with the other, Bruce, 45, pulled away and leapt out of the door, the inquest in Oxford heard.

The pair, both experienced skydivers, had been flying home from Spain after taking part in a parachuting display.

Bruce, a veteran of Northern Ireland and the Falklands, who joined the parachute regiment aged 17, had a history of mental illness and had been prescribed lithium to control depression.

He wrote a book about his experiences, entitled Freefall, under the pseudonym Tom Read. The book is described as the "true story of one man's descent into madness" and deals with suffering from post-traumatic stress disorder.

The former para, known as Nish to friends and colleagues, had not seemed particularly unwell during the flight back to England although he had been quieter than normal, Ms Haig told the inquest.

She described how the weather had deteriorated as they were flying over Fifield, Oxfordshire, and large chunks of ice had begun to form on the two-seater's wings, making it difficult to control. It was just after she requested permission to make an unscheduled landing at nearby RAF Brize Norton that she noticed Bruce was starting to slide his chair back and she heard the clink of a seatbelt buckle.

"I just seemed to have a sense of what was going on when he looked out of the window. He turned around, said a few words to me, and I asked him to help me fly the aircraft.

"He said I was doing fine - he had obviously thought it through. It all happened so fast. I heard him unbuckle his seatbelt, it's a very distinctive clink, and he tried to conceal it from me," she told the inquest. "He turned to get out. I grabbed hold of him, trying to hold on with one hand to control the aircraft, and one hand on him. There was quite a lot of movement in the cockpit."

Ms Haig told the inquest that the SAS veteran then leapt out of the door. His body was found lying at the edge of a farm field near Fifield.

Bruce had been awarded the Queen's gallantry medal in 1986 for his service in Northern Ireland, but he had claimed he was forced to leave the army two years later "because he was not a team player". He had then worked as a security adviser and bodyguard for celebrities, including the comedian Jim Davidson.

But his experiences in the special forces came back to haunt him and he suffered prolonged bouts of depression and mental illness.

In his autobiography he described how he once tried to stab his first wife, convinced she was trying to kill his only child. And in the final chapter of his book, he wrote: "Why am I so miserable? The nights are the worst. That's when I start thinking about suicide because it is the only solution I can arrive at."

Recording a verdict of suicide, the Oxford coroner, Nicholas Gardiner, said he was concerned about the handling of Bruce's medical history as well as the fact that he had been allowed to fly despite psychiatric problems. He said he would be writing to medical authorities about the matter.

"I find it impossible to discover exactly what happened on the day of Charles's death other than that he deliberately took his own life. There is nothing to suggest that Charles didn't know what he was doing so I can satisfactorily record a verdict of suicide," he said.

In a statement after the hearing, Ms Haig said of her friend: "He was a fine and rare man who generated huge affection, immense respect and great loyalty from those who were fortunate enough to know him in his whirlwind passage through life.

"He was a credit to his country which he was proud to serve with deep commitment and integrity. He will be sorely missed by all those who were closest to him."