The actor confronted Ceon Broughton, 30, in a waiting room following the prosecution’s closing speech at the rapper’s manslaughter trial.
John had stormed out of court after hearing Broughton’s negligence in letting the actor’s daughter Louella die from an overdose of hallucinogenic party drug 2C-P was `truly shocking’ and `exceptionally bad’.
As he walked passed the rapper he told him: “You’re evil…evil.”
Witnesses said Broughton ‘flipped out’, smashed a court table and damaged a water cooler before being overpowered by police.
The judge directed the jury at Winchester Crown Court should not be told of the clash in case it prejudiced the trial.
Yesterday they found the grime star guilty of Louella’s manslaughter and supplying her with the Class A drug that killed her at the Bestival music festival in Dorset in September 2017.
The judge Mr Justice Goose will sentence him on Friday.
Broughton, who has pleaded guilty to supplying 2C-P to Louella and a pal three months earlier at Glastonbury, shouted to his lawyers `text my mum’ from the dock as he was remanded in custody.
The maximum jail stretch for manslaughter is life.
John, 62, left the courtroom in tears with wife Carol, 68, after the jury of six women and five men took nine hours to convict Broughton after a month-long trial.
Outside the actor said: “Regardless of the outcome of this harrowing trial there are never going to be any winners.
“We started our life sentence on what would have been Louella’s 25thbirthday.
“Ceon’s life sentence is knowing he did not help Louella to live.”
Following yesterday’s verdicts we can reveal the dramatic details of last week’s court clash between John and his daughter’s killer for the first time.
When the actor – who also starred in Holby City, Casualty and Taggart – walked past Broughton as he sat in the public waiting area John turned to him and said: “You’re evil…evil.”
Louella’s sister Daisy, 29, then walked up to the musician and said: “Why won’t you say sorry Ceon? We just want you to say sorry.”
Eyewitnesses said Broughton let out an ‘agonising roar’, picked up a table and hurled it 30ft into the opposite wall – smashing it to pieces.
As Daisy and her dad hurried from the waiting area the rapper jumped up screaming, stormed into an ante-room outside another court and hit out at a water fountain.
Two detectives who had been involved in the trial raced after him.
A witness said: “One of them shouted, ‘let’s nick him’.
“They went into the ante-room and you could hear Broughton being restrained.
“You hear the sound of flesh on flesh.
“Thirty seconds later one of the cops came out with Broughton in a double arm lock. He was still raging saying, ‘Get the f*** off me’.
“The cop said Broughton had been hitting himself.
“He just flipped out – totally freaked out.
“He was trying to struggle free but his arms were locked behind his back.”
Broughton’s lawyer Stephen Kamlish QC sat with his arm round him for 10 minutes soothing him and urging him to return to court.
The jury heard the rapper – who had been dating Louella for a year – gave her a `bumped up’ dose of 2C-P after the pair disappeared to a wood together on the edge of the festival site when storms halted stage performances.
Instead of fetching help from the hospital tent just 400 yards away as she fell critically ill he filmed her bad trip with his mobile phone for up to six hours.
The footage of her life draining away due to exhaustion from hours of hallucinogenic ranting was so disturbing one juror asked to be discharged after viewing it.
Part of it was a sick advert for his Laigon Life vlog webpage.
Just 20 minutes before she died he used his mobile to order artwork for his London flat.
The yoga teacher, dancer and model became the first person in the world to die from an overdose of 2C-P drug since its 1975 invention just an hour before her 25th birthday.
Blood tests showed she had also taken ketamine and ecstasy.
Broughton shot three images of her dead before finally going to alert festival security – then claimed he could not find her in the forest.
The court heard he did not help her because at the time he was subject to a 24-week suspended jail sentence imposed for two charges of possessing a lock knife the month before and was terrified he would be locked up if he was caught breaking the law again.
He claimed Louella – the goddaughter of later One Foot In The Grave actor Richard Wilson – had got the drugs herself while he was tucking into a festival toastie and thought she would recover.
John and Carol, a former member of TV dance troupe Hot Gossip, had dashed 130 miles from their north London home to Bestival after overhearing their daughter ‘screeching’ like a `wild animal’ during a phone call from the scene.
But by the time they arrived she was already dead.
Despite his drug peddling the grime star known as CEONRPG – who has recorded with Skepta and Wiley – had been welcomed into the Michies’ home at Christmas because Louella was so smitten with him.
But they did not know he had an ‘interest’ in ‘death images’ and had fed two other girls drugs then filmed them in the weeks before Louella’s fatal trip.