A Thames Valley police constable has received a written warning after he was found guilty of misconduct for failing to properly observe Leroy Junior Medford, 43, who died in custody last year from an overdose of heroin.

Medford was arrested near Reading at about 1.30pm on 1 April 2017 by Thames Valley police. After he became unwell, officers took him to Royal Berkshire hospital. After he was discharged and returned to custody at Loddon Valley police station, he was found unresponsive in his cell at about 4am on Sunday and pronounced dead at 5:13am.

The officer tasked with watching Medford was subject to a misconduct meeting on Monday.

In a statement to the Guardian, Medford’s family welcomed the findings. They described Medford as a “loved brother, father and son” who was vulnerable at the time of his death.

The statement said: “His tragic death was caused by a fatal overdose of heroin after he was able to conceal and then swallow a large quantity of the drug whilst he was supposed to be under constant observation by Thames Valley police officers.”

The family added: “We cannot help but feel that the police officers’ failures to properly watch Junior and then properly consider how the drugs package could have just disappeared shows that officers disregarded Junior’s welfare and ultimately his life.”

While the family were pleased misconduct was found, they said: “It is still difficult for us to accept that, given what happened to Junior, this officer will only receive a warning.”

Deborah Coles, the director of the charity Inquest, said: “A written warning for police misconduct undermines the seriousness of the concerns raised.”

The family described the decision to allow only two family members to attend the hearing as “unfair and unacceptable”. Coles added that the restrictions on the number of family members attending the misconduct meeting “denied them that right and the importance of an open and transparent process”.

A spokesperson for Thames Valley police said: “A misconduct meeting took place on Monday (17/9) in connection with allegations of misconduct against a police constable. The misconduct was proven in respect of duties and responsibilities and orders and instructions. A written warning was issued as a result.

“Two members of Mr Medford’s family were invited to attend in accordance with police regulations and for reasons of balance, in addition to their legal representative. The chair of the meeting, a senior officer, has offered to further discuss the outcome of the meeting with Mr Medford’s family.”

An inquest into Medford’s death is set for June 2019. The family do not believe the officer in question was the only one at fault and said they looked forward to the inquest to “expose other misconduct and failures”.