Panicked passengers toppled over each other as they fled through carriages when the man launched an unprovoked attack on the stranger, the Old Bailey heard.

Attacker Ricky Morgan, 34, was heard to tell horrified onlookers: "This is not a terror attack, I only want him."

The victim, James Porritt, who suffered a severe injury to his hand, told jurors it was like a "horror movie" and the Arnold Schwarzenegger sci-fi film Terminator.

Morgan denied attempted murder on grounds of insanity but was found guilty by a jury at the Old Bailey after two days of deliberations.

Following the verdicts, police released graphic CCTV footage showing Morgan shouting and thrashing with the machete inside the carriage as terrified members scrambled to get away.

Detective Sergeant Nick Thompson, of the British Transport Police, said: "This was a brutal and unprovoked attack. The two men had never spoken, never met and had never crossed paths until that day.

"Clearly it was a terrifying situation for the victim, he was able to escape but this attack and the injuries he suffered continue to have a substantial impact on his life."

On the evening of July 9 last year, Porritt, a self-employed businessman, boarded a train at Westminster on his way to meet his girlfriend and her father in west London, when Morgan produced a machete and lock knife from his rucksack.

Porritt had been looking at his phone and feeling nervous about the family meeting when he heard a scream.

The next thing he knew was the defendant hitting him over the head, the court was told.

"I was pleading 'Please stop, please stop'," he told the jury.

"I was in shock, it was like a horror movie. I genuinely thought he was going to kill me."

Porritt said he did not feel anything but saw the blood as Morgan smashed an object over his head.

He said: "I didn't understand why this guy was hitting me. There was no confrontation. There was no issue, it was just bang, (he) started hitting me.

"He was like a machine. It was like that movie Terminator.

"He was emotionless. He did not seem to have any kind of compassion. But it seemed very focused and relentless and he was just hellbent on doing what he was doing ... I genuinely thought I was going to die.

"I just knew, fight or flight. I just ran for my life. It was like a stampede, people were terrified."

According to witnesses, passengers got up and screamed when the attacker started waving the knife around.

Many tried to run away but in the panic ended up piled on the floor, the court heard.

Morgan, who declined to give evidence in court, will be sentenced in July.

Australian Associated Press