Amer, another son and former finance student, who also travelled to Syria, is understood to be continuing to fight in the Middle East.

During his Old Bailey trial, jurors were played a video of Deghayes’ speech at the mosque on Sunday November 1 2020.

In it, he was seen to make a stabbing gesture when talking about jihad.

He told worshippers: “Whose power is more powerful than us? Allah is more powerful than you. You, idiots. You kuffar (non-believers)… The non-believer is an idiot. He’s stupid.”

He went on: “Jihad, jihad, jihad. Jihad is compulsory. Jihad is fighting by sword. That means this jihad is compulsory upon you, not jihad is the word of mouth but jihad will remain compulsory until the Day of Resurrection…”

Prosecutor Ben Lloyd told jurors that the speech was not given “innocently or naively”.

He said: “The prosecution case is clear. By the defendant’s words and gestures he was encouraging people to undertake violent jihad.

“The defendant’s speech demonstrates him to be an Islamic extremist. He is someone who believes in the use of violence in the cause of Islam.

“Or, at the very least, he was reckless in giving his speech as to whether people would be encouraged.”

The defendant, of Saltdean in East Sussex, denied wrongdoing, saying he was explaining the meaning of Jihad by the sword as self-defence.

The gesture he made was a “dance of the blade”, he claimed.

He also referred to Prime Minister Boris Johnson as wearing a face covering now after describing Muslim women as “letter boxes”.

The jury was told nothing about the Deghayes family background.

In 2017, a serious case review identified missed opportunities to prevent Deghayes’ sons from being radicalised before they were killed in Syria.

There was also little understanding of the part religion played in the lives of Abdullah and Jaffar, who were believed to have been with the al Qaida-affiliated Al-Nusra Front when they died, the review added.

The report also contained allegations that their father would wake his children up at 4.30am to study the Koran and would whip them with electrical wire or hand out other punishments if he felt they were not doing this properly.

After the review, their uncle Omar Deghayes – who was arrested in Pakistan in 2002 and spent five years in Guantanamo Bay – hit out at police, claiming they took “no action whatsoever” while his radicalised young nephews were being racially abused.

Following Deghayes’ conviction, he was granted continued bail ahead of sentencing at the Old Bailey on February 25.