Bed blocking caused mental health patients to spend more than 2,000 extra days stuck in hospital at the Northamptonshire Healthcare NHS Foundation Trust last year.
A leading charity has called for more investment in community care, to help vulnerable patients return to their homes safely.
Figures from NHS Digital show the Northamptonshire Healthcare NHS Foundation Trust lost 2,330 bed days in 2018-19 because of delays discharging mental health patients who were fit to leave hospital – the equivalent of more than six years.
Delayed discharges occur when a patient has been cleared to leave hospital but there are problems arranging their next steps.
This could include a lack of suitable housing or social care in a patient’s community.
Marjorie Wallace, chief executive of Sane, said: “The staggering rise in delays to discharge mental health patients from hospital reveals how patchy and threadbare care in the community has become.
“The suicide rate for people being cared for at home is now more than double that of patients in hospital, and there are also too many cases of people neglected and at risk because they have left hospital too early and without the support they need.”
The NHS’s five-year plan for mental health, which was published in 2016, pledged to reduce delayed discharges and focus on expanding community-based services.
But across England, patients spent 273,630 unnecessary days in hospital because of delays in 2018-19.
That’s the equivalent of 749 years.
This was lower than the previous year, but still 16% higher than in 2015-16.
According to a report by NHS Providers, long stays in mental health wards can cause successful treatment to reverse, and patients to relapse.
The National Institute for Health and Social Care also warns it can lead to crowded wards and overstretched staff, which can increase the risk of serious incidents and delay patients with acute needs being admitted.
Ms Wallace continued: “The solution is not simply to discharge people more quickly and risk unnecessary distress and loss of life, but to recreate effective community teams who can work with patients and their families as they make their transition from hospital back to their home.
“Until this happens, patients risk being discharged on a wing and a prayer that they will be able to live safely in the community.”
A spokesman for NHS England said: “The NHS is treating record numbers of patients for mental health conditions, the vast majority of which are seen and discharged in a timely manner.
“Investment in mental health funding will grow faster than the rest of the NHS budget so we can expand care in local areas making it easier to treat patients in the community and out of hospital.”