A student has been found guilty of building a bomb and leaving on the Tube, nearly blowing up North Greenwich station.

Damon Smith was 19 when he packed a rucksack with explosives and ball-bearing shrapnel and left it on the underground.

The former altar boy built the device at home with a £2 clock from Tesco with help from an al Qaida article entitled Make A Bomb In The Kitchen Of Your Mom.

Smith, now 20 years old, of Abbeyfield Road in Rotherhithe, claimed in court that it was just a prank.

The weapons-obsessed student, originally from Devon, told the court that it was only supposed to spew out smoke and that it was “something to do when he was bored”.

The jury rejected his explanation and found him guilty of making an explosive substance with intent to endanger life or cause serious injury after a two-hour deliberation today (May 3) at the Old Bailey.

On October 20 last year, Smith was caught on CCTV leaving the bag containing the bomb on the Jubilee line as it was set to travel to North Greenwich.

The driver noticed the bag but thought it was just lost property, putting it into his cab and carrying it with him.

It was only when he spotted the wires coming out of the bag did he realise what a dangerous device he was carrying.

North Greenwich station was evacuated at 11am that day. Police later discovered the device was set to go off at approximately 11.02am.

Had Smith's bomb worked, it would have exploded just as commuters at North Greenwich were being ordered off the platform, the jury heard.

The defendant went on to his university campus at Holloway and, on returning home in the evening, checked the internet for news of what he had done.

Upon his arrest the next day, the autistic student admitted making the bomb but claimed he only meant it to spew harmless smoke as a Halloween joke.

He told police he had been inspired by watching someone on a YouTube channel called Troll Station making a bomb prank.

Smith, who has autism, professed to be interested in Islam and posed next to an image of the Brussels-born Islamic terrorist alleged to have masterminded the attacks in Paris.

He admitted he had thought about putting a bomb in a park but decided it would be "more funny" to delay train passengers instead.

His lawyer, Richard Carey-Hughes QC, told jurors that Smith was no "hate-filled jihadi", saying he intended to "make something that looked like a bomb but not function as one".

He said: "If this was a serious attempt to cause mass murder and the like, would he have gone about the commission of this attempt in the way he did?

"He did almost nothing to cover his tracks, which he would have done if he was expecting a full-scale man hunt, the sort that follows a terrorist outrage. He is clearly visible on CCTV at all times.

"If he set out to make a real effective killing device, something that not only looked like a bomb but was a bomb, how could it enter his mind he could pass it off as a hoax?"

However the jury rejected his defence and now Smith awaits his sentencing.

Commander Dean Haydon, the head of the Met's Counter Terrorism Command, said: "Throughout this investigation and subsequent trial, Smith claimed that his actions were meant as a harmless prank and that the object was nothing more than a smoke bomb.

"It is hard to believe that leaving what has been described as an improvised explosive device on a tube train, on a weekday morning, can be construed as anything but an attempt to endanger life. It is fortunate that the device failed to work and that no one was injured.

"At a time when the threat level remains at severe, I find it unlikely that anyone would consider his defence as an appropriate excuse for his actions.

"The jury rightly disagreed with him and I expect that Smith will now face a significant prison sentence."

Judge Richard Marks QC adjourned sentencing until May 26 to allow time for a probation report on Smith's risk to the public and further psychiatric reports.