A 20-year-old peer shot himself in the head with his father's gun while on leave from a mental hospital.

Alexander Macrae Carnegie, Lord Rosehill, was on anti-psychotic and anti-depressant drugs for a year before his death on August 31.

On the day of his death, his younger sister Lady Sarah Rosehill picked him up from Graylingwell mental hospital in Chichester.

They went to the family estate at Haben Farm, Rogate, near Midhurst.

After playing a computer game, Lord Rosehill telephoned his father, Tory whip the Earl of Northesk, and his mother in the United States.

When his sister spoke to their mother, she said Alexander had asked her what pills to take if he wanted to die.

Shortly after the conversation, Lady Sarah found her brother dead in the attic. He had shot himself in the head.

In a statement, Lady Sarah told an inquest at Chichester yesterday: "I can guess why he took his life.

"We have had family problems before and he blamed himself for them."

The shotgun he used had been taken from a locked gun cabinet in the attic.

The Earl of Northesk told the inquest: "I knew there were guns in the house and I would try to lock the doors properly.

"Part of my security regime is if I have to hunt for the keys myself, anyone else would have to do the same."

Lord Rosehill had voluntarily admitted himself to hospital in March this year, suffering psychotic symptoms and hallucinations.

Ward consultant Dr Julia Wilkinson said Lord Rosehill felt as if "people were trying to take parts of his body".

However, doctors at the hospital said he was getting better and, for the couple of months prior to his death, had allowed him on unsupervised outings.

Recording an open verdict, coroner Roger Stone said: "I find myself struggling to find beyond all reasonable doubt that Alex wanted to kill himself.

"He could have been thinking about it or simply looking at the gun when it went off. I am just not sure he intended to kill himself on that day."