A Serbian-born Muslim student in London is facing time in prison after being found guilty of plotting to join the Islamic State and to fly the group's black flag in Downing Street.

The Guardian reported that, after a nine-hour hearing at the Old Bailey, Judge Peter Rook sentenced 20-year-old David Souaan to three years in a young offender institution.

The prosecution, led by Sarah Whitehouse QC, told the Court and juries that Souaan, whose father was a Syrian Muslim, had visited war-torn Syria in December 2013. Whitehouse also presented the court with evidence taken from Souaan's laptop and phone, both of which held evidence of the student's "extremist sympathies" and told of his brief stint as a fighter in Syria. 

The prosecutor said that he was preparing to return to the country and join the ISIS when he was arrested last year.

Police arrested Souaan in May 31 after fellow students made a complaint about his radical views on Islam. His fellow students also claimed that Souaan had showed them pictures of himself in Syria with guns.

The exchange student denied the charges. Souaan told the jury that he had gone to Syria with his father, who was from the town of Deir ez-Zor, for two days and proceeded to Turkey to "retrieve his... grandfather's belongings" afterwards.

He also defended the pictures of himself with guns while in Syria. "At the time when I was there I felt something like I wanted some trophy – the photos. As the teenagers say nowadays, it looks 'cool'," he told the jury.

Defence attorney Ali Bajwa QC pleaded for "leniency" from the court. Bajwa cited Souaan's supposed emotional naivety and immaturity, and his trauma at experiencing wars in both Serbia as a child and in Syria as a teenager.

However, Judge Rook said that, while Souaan's offence was the "lower end of the scale" and that his immaturity made him vulnerable to extremist views, the actions he took were "nevertheless serious."