A former Sainsbury's shop assistant from High Wycombe has been jailed for three and a half years for sharing Islamic State propaganda on WhatsApp.

Iftikhar Ali was aged 17 and living at home with his parents in Totteridge Drive, when he began sending extremist material on his mobile phone.

He denied 12 counts of disseminating a terrorist document and one of possessing a document likely to be useful to a person committing an act of terrorism.

But following a trial at the Old Bailey, Ali, now 19, was found guilty of all the charges.

Judge Mark Dennis QC said it was impossible to establish if anyone had in fact been encouraged to commit terrorism by what Ali had done.

But he highlighted the potential harm, adding: "The young and impressionable are particularly susceptible to such propaganda."

He said Ali would have received at least five and a half years in jail if he had been an adult at the time. He reduced the term by two years in light of his youth.

Ali was said to be friends with convicted terrorist Taha Hussain, who was filmed driving past Windsor Castle shouting "Allahu akbar" and "burn in hell".

Hussain, 21, from Berkshire, knew London Bridge attacker Khuram Butt and was jailed for four and a half years last September, for disseminating terrorist documents on social media.

In December 2015, Ali had been identified by the Prevent team but he failed to engage with them.

He was arrested on March 10 last year over a payment of £140 via Western Union to a man in Turkey, which he claimed in police interviews was for "charitable purposes".

Examination of his mobile phone revealed Ali had an avid interest in IS with material including audio files of radical preacher Anwar al Awlaki, and images of killings as well as Hussain's Windsor video.

Prosecutor Mark Paltenghi said Ali's offences spanned six months between September 8 2015 and his arrest.

He said: "It is the Crown's case that although he was young, he had already become a radicalised proponent and supporter of extreme Islamism."

Ali sent a string of audio files on WhatsApp containing nasheeds (songs), with titles such as For The Sake Of Allah and Give Our Regards To Abu Bakr and Oh Islamic State You Light The World.

Following his arrest, police also recovered an alleged terrorist document entitled Advice For Those Doing Hijrah (migration), jurors were told.

In a police interview, Ali said: "I have no links to any terrorist network. I was interested for research and curiosity purposes only as to what was going on in the Middle East. I'm not part of Islamic State or any other organisation."