Rashan Charles had been arrested on suspicion of dealing class A drugs a month before his death, an inquest into his death has heard.

Some of contents of the 48 packages seized were identical to the paracetamol and coffee wrap he choked on in the Dalston shop he was chased into by a police officer.

A search of Rashan’s grandmother’s home on June 13 2017 uncovered the suspected controlled substances in a sports bag, jurors at St Pancras Coroner’s Court were told on Tuesday.

Rashan – who was on the child protection register during his childhood and had eight previous convictions for possession of cannabis, another for intent to supply heroin in 2014 and one more for intent to supply cannabis in 2016 – was arrested on suspicion of possession of a class B drug and intent to supply class A drugs.

But it was not until two months after the 20-year-old’s death that chemical analysis of the substances revealed the light brown powder in 17 of the 48 packages was a mixture of paracetamol and coffee – in exactly the same ratio as that inside the plastic bag he swallowed. The “waxy, odd” white substance in the remaining 31 packages was a mixture of cocaine and pain killer phenacetin.

Rashan died in the early hours of July 22 last year, shortly after he was chased by a police officer and wrestled to the ground in the convenience store Yours Locally, Kingsland Road.

CCTV footage of him as he ran into the shop and put his fingers to his mouth has been played to jurors, as well as disturbing footage from the body-worn camera worn by the police officer, who has been granted anonymity and is known only as BX47.

Lawyers for Rashan’s mother and grandmother are questioning whether BX47 used unnecessary force as he grabbed Rashan from behind and pulled him to the ground.

But Ian Reid, an officer safety trainer for the Met, said the move known as the “seatbelt technique”, was acceptable for use in a situation where a suspect is evading restraint – and offered to demonstrate it himself.

A struggle ensued as the pair fell to the floor, and at this point a member of the public known as Witness 1, who has also been granted anonymity, offered assistance. He placed his knee on Rashan’s legs to keep him still as he was handcuffed. Rashan – who had been struggling and thrashing his legs around – suddenly became still with his eyes wide open.

Witness Callum McCray who had been standing in the shop entrance told the court he was so alarmed by the look on Rashan’s face that he came forwards, having “never seen someone in such a bad shape before”.

“It went from a high adrenaline arrest to noticing something was wrong and he needed help,” he said. “You could tell from the officer’s actions he was trying to work out what was wrong with Rashan, and trying to assist him. It all happened very quickly. We weren’t sure if he was having a seizure. You could see he was struggling to breathe. I had no idea he had something in his mouth. It’s only afterwards I found that out.”

Mr McCray added: “I was shocked to see some of the social media stuff afterwards. It made out it [Rashan’s death] was the force of the police officer throwing him to ground, and if I hadn’t been in the shop I’d have come to the same conclusions.”

Footage shows the officer then telling Rashan to “spit it out” eight times, and to “breathe”.

Witness 1 asked people in the store to find a “chocolate bar” to keep open Rashan’s mouth.

BX47, who has already admitted failing to follow parts of his first aid training, did not immediately call an ambulance but called for back up from his colleagues.

“If you think they’ve swallowed the drugs you’re in the region of a medical emergency and you call an ambulance,” said safety trainer Mr Reid.

Mr Reid said it is also permissible to accept the help of a member of the public for restraint during an arrest – but would have asked witness 1 to get up once the handcuffs were on.

“If I was in that situation it would distract me from my thought processes,” he said. “But I may have been distracted by the fact he was a first aider.”

He would also have removed the handcuffs once he realised it was a medical emergency.

“The main thing in a stressful situation is to see everything that’s going on,” he said. “Quite early on in the restraint, you see Mr Charles glug on his side. I’ve seen that because I’ve watched the film several times. The starting eyes.

“But if I’m in that situation where I’m trying to control Mr Charles and he’s resisting, then my main objective is to get him into handcuffs. It’s easy to say that in hindsight and sometimes you get tunnel vision and you don’t see the whole picture, but the main thing is to step back and see what’s going on.”