A notorious British extremist known as the Supermarket Jihadi is believed to have killed himself in a suicide attack in Syria, The Mail on Sunday can reveal.

Omar Hussain took part in a ‘martyrdom operation’ when ISIS was under siege in its then de facto capital Raqqa in northern Syria as the group fought a last-ditch battle against Western-backed Kurdish forces, it is understood.

Security sources have told the MoS that reliable intelligence has emerged that Hussain – who became one of the most high-profile British ISIS jihadis in Syria – has died in the war. One source said that he volunteered for the suicide mission because he realised he could not return to Britain.

Hussain, who would now be 32, used to work as a security guard at his local Morrisons store in High Wycombe, Buckinghamshire, fled to Syria in December 2013, after catching a flight from Gatwick to Turkey.

Omar Hussain took part in a ‘martyrdom operation’ when ISIS was under siege in its then de facto capital Raqqa in northern Syria

His escape from Britain was hugely embarrassing for British counter-terrorism police at the time as he was already known them by then as an extremist who the authorities stopped going to Syria six months earlier.

Once in Syria, Hussain used the noms de guerre ‘Awlaki’ and ‘Abu Saeed Al-Britani’. He ran a series of blogs and social-media sites where he gave an account of what life was like in Syria, sometimes complaining that he missed his mother’s cooking, fish and chips and Jaffa Cakes.

He tried to groom and recruit many young men and women from the UK as well as raise money for ISIS from British sympathisers by telling them to steal and rob from non-Muslims, especially drunk revellers during Christmas.

During an investigation by The Mail on Sunday in 2015 he tried to persuade an undercover reporter to send money to ISIS. As a result of this investigation an extremist fundraiser was jailed for four years.

His escape from Britain was hugely embarrassing for British counter-terrorism police at the time as he was already known them by then as an extremist who the authorities stopped going to Syria six months earlier

Hussain, who would now be 32, used to work as a security guard at his local Morrisons store in High Wycombe, Buckinghamshire

Hussain achieved notoriety after giving an interview to the BBC in 2014 when he spoke of his loathing for Britain. He said: ‘I hate the UK, the only reason why I would intend to return to the UK is when I want to come and plant a bomb somewhere.’

In the same interview, he admitted to beheading several people in Syria, and displaying their severed heads in the city of Aleppo, parts of which ISIS then controlled. Only weeks later, he issued another video in which he called then Prime Minister David Cameron a ‘despicable swine’.

Hussain was one of only four British jihadis in Syria to be placed on a UN sanctions list. The Home Office is believed to have stripped Hussain of his UK citizenship to prevent him from returning to the country.

British journalists who visited Raqqa after its liberation from ISIS at the end of 2017 found his nom de guerre, Abu Saeed Al-Britani, scrawled on the wall of a prison cell under the city’s sports stadium.

Hussain was one of only four British jihadis in Syria to be placed on a UN sanctions list

Digits scrawled under his name, numbering 49, suggesting Hussain may have been imprisoned for that many days in the jail, which was notorious as a place of torture and executions. Experts said at the time that it was unlikely Hussain would have survived his detention. He was held after angering ISIS leaders by urging Britons to join its branches in Libya instead of Syria.

But now sources say they have received strong intelligence that he took part in a suicide attack.

Residents near his family home in High Wycombe said that they had heard rumours that he was killed in Syria, though one said: ‘His mother still has hope that he is alive and will come back one day.’

Hassan Bal, 27, was jailed last year in Ireland as a result of the 2015 MoS investigation. During the trial, judge Eugene O’Kelly said: ‘I would like to recognise the role of the investigative reporter at The Mail on Sunday in this case and the importance of a free press in a democratic society.’