A Twitter user claims to have pranked the Daily Mail with a story about a white British teenage boy who purportedly joined Islamic State after failing to get a university place.

The story, headlined Who is Britain’s white jihadi youth?, first appeared on MailOnline on Boxing Day and showed a photograph posted on Twitter of the teenager, said to be called Jonathan Edwards, sitting between two jihadi fighters in front of an Isis flag and clasping a rifle. The story also appeared in the newspaper on Saturday.

Twitter user Abu Dawud – who posted the picture with the caption, “Meet Jonathan Edwards – applied for Ucas to [sic] late and wasn’t accepted in any university, so he joined the Islamic state” – gleefully claimed on Saturday that the article was a hoax, adding that he had successfully “trolled” British media.

Daily Mail newspaper article headlined Mystery of white jihadi with the baby face. Photograph: Twitter

The picture was first posted at the beginning of December by ResistanceER, who wrote: “Creepy Isis. Soldier in their rank of ‘Brave and well Trained’ soldiers.” It was then tweeted again by Abu Dawud, a blogger who claims to be based in Yemen.

“My trolling made Daily Mail,” he said in one tweet. “I lied Wallah.” He added: “I humiliated the British media all by myself. I am a lone wolf.”

His revelation also brought derision on the newspaper from an anti-terrorism expert. Shiraz Maher, a senior fellow at the International Centre for the Study of Radicalisation at King’s College in London, tweeted on Saturday that it had repeatedly warned that the story was fake.

I humiliated the British media all by myself, I'm a lone wolf! Pay me💰 — Abū Dāwūd (@_AbDwd1) December 27, 2014

He wrote: “The ‘jihadi’ Jonathan Edwards story should be a lesson to the media to verify Syria news before publishing. We constantly said this was fake. If the Daily Mail had done even rudimentary research, they’d have realised the Ucas deadline is 15 January. As @_AbDwd1 has shown, if you wave ‘white English convert’ and ‘scary Muslims’ in the Daily Mail’s face, they’ll run it regardless of facts.”

Maher earlier told the Telegraph: “I don’t think there’s enough evidence to say it’s a British fighter or that the picture is 100% authentic. There aren’t many white English converts in Syria. If he’s happy to sit there with his face uncovered we’d have seen it in a bigger propaganda hit.”

Isis has drawn recruits from all over the world, including up to 500 Britons believed to have travelled to Syria to join the militants. The extremist group has also demonstrated a sophisticated use of social media and modern technology for propaganda purposes.

The counter-extremism thinktank Quilliam was said to be investigating whether the picture was authentic or not.

Managing director Haras Rafiq told the Mail: “I have not come across this picture before. It is also strange that one post has called him ‘Jonathan Edwards’, rather than him taking on an Islamic name. But having said that, I am not going to discount it.”

On Saturday the Mail had updated its online story to say there was “speculation that the photo could be a sophisticated fake”.