A father whose son took his own life in July 2020 is calling for an "urgent overhaul" of the way some counsellors and therapists assess suicide risk.
His son Tom had died a day after being judged "low risk", in a final counselling session, Philip Pirie said.
A group of charities has written to the health secretary, saying the use of a checklist-type questionnaire to predict suicide risk is "fundamentally flawed".
The government says it is now drawing up a new suicide-prevention strategy.
According to the latest official data, 6,211 people in the UK killed themselves in 2020. It is the most common cause of death in 20-34-year-olds.
And of the 17 people each day, on average, who kill themselves, five are in touch with mental health services and four of those five are assessed as "low" or "no risk", campaigners say.
Tom Pirie, a young teacher from Fulham, west London, had been receiving help for mental-health issues.
He had repeatedly told counsellors about his suicidal thoughts - but the day before he had killed himself, a psychotherapist had judged him low risk, his father said.
Tom's assessment had been based on "inadequate" questionnaires widely used despite guidelines saying they should not be to predict suicidal behaviour, Philip said.
The checklists, which differ depending on the clinicians and NHS trusts involved, typically ask patients questions about their mental health, such as "Do you have suicidal thoughts?" or "Do you have suicidal intentions?"
At the end of the session, a score can be generated - placing the individual at low, medium or high risk of suicide, or rating the danger on a scale between 1 and 10.
Source: BBC News, 20 April 2022