A lack of effective clinical leadership contributed to the death of an 18-year-old man at a mental health unit in Oxfordshire, an independent report has concluded.

Connor Sparrowhawk, who drowned in the bath at an assessment and treatment centre run by Southern Health last July, was found to have been the subject of several failures of care.

The trust had suggested Mr Sparrowhawk could have died from “natural causes”.

Mr Sparrowhawk had Klinefelter’s syndrome, which led to learning difficulties, autistic traits, epilepsy and seizures.

An investigation by the firm Verita, commissioned by the trust, found staff at the Slade House site in Headington failed to properly risk assess Mr Sparrowhawk’s epilepsy.

This oversight led to “a series of poor decisions around [Mr Sparrowhawk’s] care”, the report found. The specification in his care plan that he should be checked only every 15 minutes while in the bath was found to be inadequate.

Sara Ryan, Mr Sparrowhawk’s mother, said of the report: “We encourage people to read it, and to remember that Southern Health were quick to write Connor’s death off as natural causes and that all due processes were followed.”

“He should never have died and the appalling inadequacy of the care he received should not be possible in the NHS.”

Minutes from a board meeting which took place shortly after Mr Sparrowhawk’s death said: “The postmortem indicates the user died of natural causes and early investigations indicate all appropriate systems and processes were in place and being followed leading up to the incident.”

The trust’s deputy chief executive Sue Harriman apologised for “any unfortunate wording in the board reports”.

She added: “There was an immediate management response – epilepsy management was identified as an issue in the initial incident report 48 hours after the death.”

The Care Quality Commission issued an enforcement notice to the trust last November after an inspection found its Headington site was in breach of six essential standards. These included standards relating to the care and welfare of service users, cleanliness and the safety of premises.