A prison that a coroner has described as "at breaking point" left a high-risk prisoner alone for two hours before officers found he had hanged himself.
Daniel Dunkley, of Ermine Road, Northampton, tried to take his own life in his cell at HMP Woodhill, in Milton Keynes, in July 2016. He died in hospital six days later.
A jury ruled at an inquest on April 28 that Mr Dunkley's death was caused by HMP Woodhill's failure to learn from previous inmate suicides.
Deborah Coles, director of INQUEST Lawyers Group, said: “The unbroken pattern of Woodhill deaths reveals a systemic failure at a local and national level to act in response to critical inquest findings and recommendations for action. This raises serious questions about the accountability at senior management level of those responsible for prison health and safety."
Mr Dunkley was the 16th of 18 prisoners who have taken their own life while at the prison since 2013. HMP Woodhill currently has the highest number and rate of deaths for prisons in England and Wales.
He was high-risk status and had made threats to take his own life on the day he hanged himself. But when he was found, no one had checked on him for almost two hours.
The jury's conclusion made a number of severe criticisms of HMP Woodhill, including that staff failed to follow-up on Mr Dunkley when he did not attend an urgent mental health assessment on the day.
Yet on the day he hanged himself, a senior officer assessed Mr Dunkley as 'low risk'.
Three inexperienced staff were left to work unsupervised on Mr Dunkley's wing and mandatory observations were not carried out, as only two of them were told about Mr Dunkley's threats to take his life.
The jury concluded that the prison failed to carry out suicide prevention procedures and contributed to his death through neglect.
The acting governor of HMP Woodhill, Ms Marfleet, accepted 'a litany of serious failings in Mr Dunkley's case that were completely unacceptable'.
HM senior coroner for Milton Keynes, Thomas Ralph Osborne, described HMP Woodhill as an organisation at "breaking point".
Deborah Coles said: "HMP Woodhill and the prison service have repeatedly failed to implement recommendations in the face of a litany of failures. They have clearly ignored warnings about the risks to the health and safety of prisoners, and the necessary sanctions should be enacted against those responsible.
"All politicians need to address the issues behind this broken and dangerous system and the unacceptable death toll.”