The police watchdog is investigating a custody officer over an alleged missed welfare check after a man died in a police cell in Croydon. Jason Mattison, 52, was found unresponsive at the Windmill Road Custody Suite in the early hours of 21 August.

The Independent Office for Police Conduct (IOPC) has served a notice of investigation on a designated detention officer, a member of custody staff. The officer is alleged to have failed to carry out a scheduled welfare check and to have incorrectly recorded that the check had taken place.

What happened at Windmill Road

Mr Mattison had been arrested in Croydon on Wednesday 19 August on a no-bail warrant issued by Croydon Magistrates' Court, after he failed to appear on charges of being drunk and disorderly. He was held at Windmill Road Custody Suite while awaiting a court appearance.

Officers carrying out cell checks found him unresponsive at around 00:30 on Friday 21 August after he became unwell. Custody staff and paramedics gave emergency first aid, but he was pronounced dead at 01:17. The Metropolitan Police said he had been seen by a healthcare professional and had received welfare and observation checks while in custody.

Mr Mattison was subject to half-hourly welfare checks, the IOPC said. A post-mortem examination has been carried out, with further tests planned to determine the cause of death.

Officer under investigation

A notice of investigation means the officer is under investigation. It is not a finding of wrongdoing, and no charges have been brought. The IOPC said its investigation will examine the circumstances of the death, including the welfare checks carried out while Mr Mattison was in custody.

Amanda Rowe, the IOPC's director of engagement, said: "This was a tragic incident in which a man has sadly died, and our thoughts are with Mr Mattison's family and loved ones." She added: "When someone dies in police custody, it's important that a thorough and independent investigation is carried out to examine all the circumstances."

Ms Rowe said the IOPC had met Mr Mattison's family to explain its role and would keep them informed as the investigation progresses.

How custody deaths are investigated

When someone dies in police custody, the case is referred to the IOPC, which investigates independently of the force involved. The Metropolitan Police made a mandatory referral to the IOPC after Mr Mattison's death, and its Directorate of Professional Standards was also informed.

Deputy Assistant Commissioner James Harman said at the time: "Our thoughts are with the man's family and loved ones following his tragic death. The full circumstances of this death in custody will now be independently examined and we are providing our fullest support to that IOPC investigation."

Once its investigation is complete, the IOPC will decide whether there is evidence of misconduct or criminality. It can recommend disciplinary proceedings, refer a case to the Crown Prosecution Service, or make recommendations to prevent a similar death. Deaths in police custody are also examined by a coroner at an inquest.

Welfare checks are a routine safeguard in custody suites, where detainees are checked at set intervals and each check is recorded. The allegation in this case is twofold: that a scheduled check did not take place, and that the custody record wrongly showed it had.