Hundreds of patients who died while detained under the Mental Health Act may have been denied inquests, an investigation has found.

All such deaths are supposed to be reported to a coroner so they can be investigated.

But official figures show that that of 1,115 cases recorded by the NHS over three years, just one in three were reported to coroners.

Charities said the figures were “alarming” and raised the risk that deaths were not being properly investigated, to reduce the risk of future tragedy.

Brian Dow, from the charity Rethink Mental Illness, said: "If incidents are not being appropriately referred and examined then lessons can't be learnt about how to avoid further tragedies in the future.

"We owe it to people detained under the Mental Health Act and their families to ensure this.

"We want to see a robust, independent and transparent system for investigating deaths in mental health settings, so no more families are left without answers."

Official Ministry of Justice figures analysed by Health Service Journal show that between 2011 and 2014, 373 deaths of people detained under the Act were reported to coroners in England and Wales.

But data supplied to the Independent Advisory Panel on Deaths in Custody show 1,115 deaths - 742 more than those reported to coroners.