Rashan Charles “most likely” died because he tried to swallow a package that blocked his airway, causing his heart to stop, investigators have said.

A pathologist found the 20-year-old dad-of-one had “no other significant injuries to the head, neck or torso that would suggest prolonged or excessive restraint in the lead up to his death”, according to the Independent Office for Police Conduct (IOPC).

Rashan was restrained by police on the floor of Yours Locally in Kingsland Road, Dalston, on July 22.

Police watchdog the IOPC, formerly the IPCC, has released the post mortem result today, after the Crown Prosecution Service (CPS) yesterday announced the officer who tackled him to the floor and handcuffed him would face no criminal charges.

Rashan’s family said in a statement they “do not understand” the decision and that CCTV from the store showed the officer used “unnecessary force”.

The IOPC previously said the officers had tried to remove what turned out to be a package of caffeine and paracetamol wrapped in cellophane from Rashan’s mouth or throat after he was detained.

He then became “unwell” and died soon after being taken to the Royal London Hospital. The post-mortem results indicate Rashan died of cardiac arrest brought on by a blocked upper airway.

“This was, in the pathologist’s view, most likely caused by him attempting to swallow a plastic package that subsequent forensic testing showed contained a mixture of caffeine and paracetamol,” a spokesman said.

“We are awaiting further expert evidence before conducting a full review of all evidence gathered to date, including body-worn video from 10 officers, including the one involved in the restraint.”

Footage of the incident surfaced online hours after Rashan’s death in the early hours of July 22. It sparked protests outside Stoke Newington police station and clashes with riot police in Kingsland Road.

The CPS had been considering a common assault charge against an officer based on evidence provided by the IOPC.

But a CPS spokesperson said: “The CPS has considered the matter and decided the evidential test for a prosecution for common assault is not met.

“We will therefore not be taking any further action regarding this offence.”

The IOPC also said there had been conflicting advice given to officers around the country over searching people suspected of putting drugs or other packages in their mouths.

Some advice stated it was never appropriate due to the risk of choking, while other guidance said it may be appropriate in certain circumstances.

The watchdog said it had asked the National Police Chiefs’ Council (NPCC) and the College of Policing (CoP) to review their guidance urgently to ensure it prioritised the safety of the person.

As a result, the Met has suspended searching mouths by force and the CoP will be conducting a review of their guidance.

Rashan’s family issued a statement following the CPS’s announcement. They said: “The family do not understand the CPS’s decision not to prosecute this officer for even a low level common assault.

“The CCTV shows a police officer taking very forcible hold of Rashan from behind, putting him to the ground and handcuffing him.

“To us, this seems to show an unnecessary use of force. For there to be public confidence in policing we call for due process in the form of a criminal trial.

“We are aware that the IOPC has also raised concerns about police training in mouth searches, but this should not detract from the question of whether this officer acted lawfully, and if not, whether this played a part in Rashan’s untimely death.”

An inquest is scheduled for June 4. In November, senior coroner Mary Hassell granted anonymity to two Met officers who were involved in Rashan’s restraint.

Both officers – one of whom is currently on “restricted duties”, meaning he doesn’t have contact with members of the public – will be hidden from the public gallery and will only be referred to as BX47 and BX48 at the inquest at Poplar Coroner’s Court. Anonymity was also given to two witnesses.

Scotland Yard said it was aware of the CPS’s decision and did not want to comment further.