We would hope that by highlighting the fact that someone they know well could be affected by suicidal thoughts will help tackle the stigma of mental health problems

Richard Brook, Mind

They were asked whether they had ever thought that life was not worth living, or whether they felt they would be better off dead.

The sample was also asked whether they had ever attempted suicide, or if they had deliberately harmed themselves in any way but not with the intention of committing suicide.

Just over 4% of people questioned said they had attempted suicide - about half a per cent in the past year.

Some 2% of those taking part had deliberately tried to harm themselves - but without suicidal intent.

Of those currently suffering depression, a quarter had at one time attempted suicide compared with 2% of those with no current mental disorder.

Psychosis was the factor which had the highest relevance to the likelihood of suicidal thoughts, followed by the number of stressful life events endured by the person.

Schizophrenia is one illness which can lead to psychotic episodes - as can Alzheimer's disease or manic depression.

Richard Brook, chief executive of the mental health charity Mind, said: "Revelations that as many as 15% of adults have at one time or another considered suicide come as no surprise to Mind.

"We would hope that by highlighting the fact that someone they know well could be affected by suicidal thoughts will help tackle the stigma of mental health problems, and make people more sympathetic to those experiencing problems."

Dr Evan Harris, Liberal Democrat health spokesman, said the figures suggested the government had taken its eye off the ball on its strategy for reducing suicides.

He said: "The government urgently needs to consider improvements to mental health services across the board. Mental Health has often been a Cinderella service, receiving less attention and less funding."