The mother of a “white boy from Devon” who left a bomb on a London underground train has called for YouTube to be banned, blaming the video sharing platform for corrupting her son.

Student Damon Smith, 20, faces years in prison after being found guilty of planting a home made device containing ball bearings on a Jubilee Line train. Jurors at the Old Bailey rejected his claim that the device was a smoke bomb meant only to stop the train for “a bit of fun”.

Smith, who has Asperger’s Syndrome, built the device using instructions found in an Al Qaeda entitled ‘Make A Bomb In The Kitchen of Your Mom’, sourced via Google. The court heard that he had an interest in weapons and in Islam, collecting photographs of prominent Islamic terrorists and posing next to an image of the mastermind of the 2015 Paris attacks.

But prosecutors declined to charge him with terrorist offences as there was no evidence to suggest that his actions were taken to further a political, ideological or religious cause.

Addressing jurors, his lawyer, Richard Carey-Hughes QC, said that Smith was not a “hate-filled jihadi”, but merely a “white boy from Devon” who was “tied to his mother’s apron strings”.

The court heard that, had the device gone off, it would have detonated as passengers were being evacuated from North Greenwich Station.

Speaking to the Telegraph, his mother, Antonitza Smith, 47, blamed YouTube for influencing her son, saying: “How to make a bomb – that shouldn’t be on YouTube because people copy, especially vulnerable people.

“Whatever people put on YouTube, broadcast on YouTube – how to make a bomb, how to blow up a car, hacking etc – it’s illegal really. They talk about terrorism, beheadings. That shouldn’t be on YouTube so young kids could see it. It’s wrong.

“The government should ban it so it might save another child from what my son has gone through.”

Asked what sparked her son’s interest in extremism, Smith replied: “It all started off, he got interested in the Quran when he was taking his GCSEs. So my mum bought a Quran for Christmas for him and he got interested in all the predictions. That was what he was interested in mostly.

“I don’t know why he was interested in bombs. I suppose it was being a boy and his Asperger’s as well.

“Maybe a couple of years ago I noticed. He was showing me how to make bombs but I knew he was safe at home.”

Damon’s Asperger’s, combined with a high-pitched voice and babyish way of speaking led to him being bullied, which he dealt with by turning to his computer.

“As Damon has got Aspergers, he has got access to weird sorts of topics on the internet,” Ms Smith said.

“Because people with learning disabilities, if they get these funny ideas, they start copying. It can be dangerous especially if you have got autism.

“He is like a little baby. He can’t talk properly.

“I think YouTube is poison. They talk about terrorism, beheadings. That shouldn’t be on YouTube so young kids should see it. It’s wrong.”

YouTube has denied culpability. “We do not allow bomb-making videos on YouTube and if there’s content giving instruction on how to carry out harmful activities on the platform, we quickly remove it when it’s flagged,” a spokesperson said.

Sentencing has been adjourned until May 26 by Judge Richard Marks QC to allow time for reports into the risk Smith poses to the public and further psychiatric assessments to be prepared.