A police watchdog has launched an investigation into the death of a psychiatric patient who fell into a coma when he was restrained by seven policemen.

Kingston University student Seni Lewis, 23, believed to be from South Norwood, had been a patient for just a few hours at the Bethlem Royal Hospital in Beckenham when he became so violent that staff had to call the police.

Officers arrived at 9.30pm and tried to subdue Mr Lewis who “became passive” and then “seriously unwell” during the incident, according to the Independent Police Complaints Commission (IPCC).

He was rushed to Croydon University Hospital after slipping into a coma from which he never recovered. He died after his life support machine was switched off on September 4.

He was detained under the Mental Health Act.

An IPCC spokeswoman said: “CPR was started and an ambulance was called. Mr Lewis was taken to the Croydon University Hospital. On Friday September 3, the first set of brain-stem tests were performed and confirmed brain-stem death. A second set of tests were performed and as a result life support was discontinued on Saturday September, 4 2010.”

IPCC Commissioner Rachel Cerfontyne said: "I cannot even begin to imagine how difficult this must be for this young man's family. The IPCC is looking into the police response to determine whether or not it was proportionate and reasonable in all the circumstances."

A spokesman from the South London and Maudsley NHS Foundation Trust said: “A patient receiving treatment at the Bethlem Royal Hospital was transferred to Croydon University Hospital on August 31 for urgent medical treatment and sadly passed away on the evening of Saturday September, 4.

“We would like to extend our sincere condolences to the family of the deceased. The Trust is investigating the incident as a priority and is working closely with the police. It would not be appropriate for us to comment further at this stage.”

A preliminary autopsy has been carried out but the cause of death remains unknown.

An inquest has been opened and adjourned at Croydon Coroner's Court.

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