The British ISIS fanatic accused of being the 'new Jihadi John' is a former Arsenal and Nirvana fan who fled to Syria while on bail and was put in charge of promoting the Islamic State to tourists.

Hindu-born Londoner Siddhartha Dhar, 32, was known as 'Sid' to friends and enjoyed drinking, would take girls to his favourite action movies and dreamed of being an NHS dentist.

MI6 and foreign secret services are now trying to work out if he is the new Jihadi John - and has already earned the nicknames 'Sid Vicious' and 'Jihadi Sid'.

Dhar's family say he was a 'sensitive boy' who 'changed' as a teenager after the death of his father and converted to Islam, shunning TV and music, sleeping on the floor and even telling his mother he couldn't love her anymore because she is not a Muslim.

He stopped studying and rented bouncy castles for children's parties while supporting banned militant group Al-Muhajiroun and running 'roadshows' aimed at attracting troubled youngsters in inner-cities.

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Number one suspect: The ISIS executioner dubbed the 'new Jihadi John' (left) is believed to be British fanatic Siddhartha Dhar, also known as Abu Rumaysah (right) who taunted police after skipping bail to flee to Syria

Chilling: This is Siddartha Dhar, the man believed to be the new Jihadi John, pictured with one of his five children whown here clutching his father's handgun after settling in Syria last year

Life in Britain: Dhar discussed his former bouncy castle rental business in a VICE documentary in June 2013, his job while supporting banned groups and marching for Sharia law in Britain before he fled while on bail

Life's work: Dhar, who took the name Abu Rumaysah, wrote an English language guide to life under ISIS aimed at encouraging other Britons to come and join him in the caliphate

After his arrest last year for encouraging terrorism he was forced to hand in his passport and put on a terror watchlist.

But despite his lack of travel documents and links to numerous known extremists, within 24 hours he travelled by bus to Paris, and then on to Syria with his pregnant wife and four children.

Dhar then wrote ISIS' 46-page guide to life in the caliphate promising a holiday lifestyle with home comforts.

He said the Islamic State was like a 'plush Mediterranean resort' with British chocolate like Kit Kats, Bounty bars and Snickers freely available 'and the best lattes and cappuccinos around.'

Photographs have emerged of the British ISIS fanatic Siddhartha Dhar at a series of Islamist rallies in London, pictured here on the tenth anniversary of the 9/11 attacks outside the US Embassy in London

The book's cover shows his name with al-Britani on the end - used by jihadis to say they are from Britain - and the picture is ISIS troops firing at Jerusalem as they march on the Israeli city.

His 46-page guide to the Islamic State covers everything from weather, food and transport to education, people and technology.

He writes: 'Snickers, Kit Kat, Bounty, Twix, Kinder Surprise, Cadburys - yes, yes we have it all.

'If you were worried about leaving behind your local Costa coffee then you will be happy to know that the caliphate serves some of the best lattes and cappuccinos around.'

Describing the country's weather, the ISIS fighter says: 'This really depends on where you are, but as it stands the caliphate offers an exquisite Mediterranean climate that has all the makings of a plush holiday resort.'

In it he also boasts of the 'education' offered in the caliphate: 'There are no classes promoting homosexuality, evolution, music, drama, interfaith and the rest of the rubbish taught in non-Muslim schools. Your child's delicate mind is well and truly protected in the caliphate.'

He writes that the caliphate 'screams diversity' and has become a 'magnet for talent'.

'If you thought London or New York was cosmopolitan then wait until you step foot in the Islamic State,' he writes.

His sister Konika Dhar said last night: 'I am going to kill him' if it's found he is the new Jihadi John.

She has previously described how her brother was a typical teenage boy known to friends as 'Sid' who enjoyed football, blockbuster films, dating girls and drinking Baileys to mark special occasions.

He also had a passion for rock bands Nirvana and Linkin Park.

One school friend told MailOnline he was 'an incredibly quiet boy who never ever got into trouble'.

She said: 'He had a few friends but was pretty much a loner, never one of the popular kind of boys. He had hardly any confidence and was pretty much forgettable. It seems to me he's only become this type of person for attention'.

After their father died when he was 16 he decided to drop out of school, taking jobs in Boots and later as a bouncy castle salesman.

Meanwhile he met and married his wife Aisha, then 23, and the couple have five children, including one called Usama, named after Osama bin Laden.

Siddhartha's former neighbours in Walthamstow, north east London, suggested his wife may have helped radicalise him and others.

Wife Aisha Tariq has previously been said to have influenced her older sister, also from Walthamstow, travelling to the Middle East with her husband and their four children in August.

Her husband would go to the Finsbury Park Mosque to hear extremist cleric Omar Bakri Mohammed preach and was a familiar face at anti-West marches in London and was one of the ringleaders of a protest outside the US Embassy on the tenth anniversary of 9/11.

Dhar, also known as Abu Rumaysah, is believed to have met, and possibly mentored, Michael Adebolajo, one of the murderers of Fusilier Lee Rigby.

He also joined and supported Muslims Against Crusaders, which counted some of Britain's best known extremists including Abu Izzadeen and Abdul Haq as members.

Izzadeen was jailed for more than four years for terror offences and was recently arrested in Europe trying to get to Syria while Haq helped terrorise Muslim shopkeepers in east London who wanted to sell alcohol.

Taunting the police: Abu Rumaysah posted a picture of him cradling his baby and brandishing an assault rifle in the other to mock security services whose blunders allowed him to escape the UK

Pledge: Dhar promised people who come to join ISIS in Syria or Iraq home comforts, including their favourite chocolate bars

Big sell: A section of his 46-page book says the Islamic State has 'all the makings of a plush holiday resort' in the Med

'Education in the caliphate': Al Britani tries to reassure parents that 'your child's delicate mind' is protected in this section of his guide

As Britain tries to unmask the new Jihadi John it has emerged:

Former bouncy castle salesman Siddhartha Dhar, 32, believed to be British executioner in new ISIS video

Hindu-born Dhar, who took the name Abu Rumaysah after converting to Islam, was able to leave Britain despite being on bail for terror offences

Prime Minister David Cameron may target Dhar in a drone strike in Syria 'to protect British people' at home and abroad

The grandfather of the British boy dubbed Jihadi Junior tells how the four-year-old begged to be rescued in a heartbreaking phone call just days before he was forced to appear in a sickening ISIS execution video

Henry Dare, 59, accused ISIS of using his grandson Isa Dare 'as a shield' and urged his extremist daughter, Grace 'Khadija' Dare, to return to Britain to 'face the music'

Video emerged showing Dare boasting in a documentary two years ago about her new life as a jihadi bride in war-torn Syria as she goes shopping for nappies with an AK-47 slung over her shoulder

Dhar, 32, was released on bail after his arrest in September 2014 and ordered to hand in his passport.

THE RACE TO CONFIRM IF THE NEW JIHADI JOHN IS 'SID VICIOUS' Britain's security services are today using advanced technology to confirm for sure if ISIS' new executioner is Londoner Siddhartha Dhar, 32. The UK has for some time been flying its spy plane Airseeker over Syria and Iraq intercepting ISIS communications and trying to find British voices. The drone is controlled by pilots based at RAF Waddington in Lincolnshire and all the recordings of interest are banked and sent to GCHQ's headquarters in Gloucestershire for analysis. The many hours of recordings are now being compared to the British voice on the new ISIS execution video - and will be matched to a jihadi likely to be known to MI5 or MI6. But Government sources have said that Dhar, also known as Abu Rumaysah, is only one of a small number of people likely to be behind the mask. Security services have completed an 'initial assessment' of the identity of the masked jihadi but the Prime Minister's official spokesman said that agents are not expected publicly to confirm the identity of the man. She declined to say whether David Cameron would be ready to order an RAF drone strike to kill the militant, as he did with British national Mohammed Emwazi - known as Jihadi John - in November. But she added: 'The Prime Minister has spoken before and it remains his view that he will look at what action is necessary to protect British people in this country and to protect us from the threat posed by Daesh.' Advertisement

He was among nine men detained on suspicion of encouraging terrorism and supporting the banned group Al-Muhajiroun.

But less than 24 hours after walking free, he was able to get on a coach from London to Paris and headed to the ISIS war zone with his young family.

The former bouncy castle salesman later posted a picture of himself cradling his baby while brandishing an AK-47 to taunt security services whose blunders allowed him to escape.

Prior to posting the photo, Dhar taunted the police on Twitter for clumsily allowing him to slip through their fingers: 'What a shoddy security system Britain must have to allow me to breeze through Europe to the Islamic State.'

He also boasted how he had fooled MI5: 'My Lord (Allah) made a mockery of British intelligence and surveillance. Make hijrah (flight) Muslims. Place your trust in Allah'.

Now it appears he has volunteered to become ISIS' executioner-in-chief after Jihadi John was 'vapourised' by an American drone missile in December.

MI6 are now racing to identify whether he is the militant with an English accent in a new ISIS execution video where five alleged British spies were killed and he was seen shooting one in the head.

It means that Dhar, if it is him, will be at the top of Britain's 'kill list', which contain's the names of the UK's most dangerous jihadis currently fighting in Syria.

His family have called on him to return to Britain to be 'deradicalised' but admit that they might attack him themselves.

His sister, Konika Dhar, from North London, said: 'If it is him, bloody hell am I shocked? I am going to kill him myself. He is going to come back and I am going to kill him if he has done this.

'I can't believe it. This is just so shocking for me. I don't know what the authorities are doing to confirm the identity, but I need to know if it is.'

His mother said she could not be sure of it was her son but was shocked by the revelations, and never suspected he had terrorist links, describing him as 'sensitive and shy'.

Speaking at her home mother Sobita Dhar said: 'These are the most difficult questions to answer - I just cannot say. I'm not sure within myself whether it's the truth or not.

'I last saw him before he went off to Syria two years ago.'

'I am going to kill him myself': Dhar's sister, Konika, admitted the voice in the ISIS execution video sounded 'a bit like' her brother, but did not believe it was him

Siddhartha Dhar (pictured, far right, at a rally) was one of nine men detained on suspicion of encouraging terrorism and supporting the banned group Al-Muhajiroun

A few weeks before his arrest, he told one interviewer that he was willing to renounce his British citizenship if it meant he was allowed to travel.

Online news magazine VICE, which interviewed Dhar in 2014, claimed the executioner's 'voice and speech pattern' was similar to the British fugitive.

Speaking in the documentary titled Escape To The Islamic State, Dhar recalls the bouncy castle business he ran in the UK before becoming a jihadist.

Several Twitter users, including respected Al Rai correspondent Elijah Magnier, have also raised the possibility he is the killer militant.

It is possible that a different voice was dubbed over the footage after it was filmed.

However, linguistics expert Jane Setter believes the militant was speaking at the scene.

The Reading University professor told MailOnline: 'Unlike the Jihadi John video, the movements of the speaker's jaw are much more discernible.

'This leads me to believe he is most likely speaking 'live' and not that the masked face has been overdubbed later.'

Well known: British citizen Dhar protested across London and other parts of the country, while being watched by police and probably the security services, but was still able to leave the UK while on bail

Campaigners: The Muslim convert (pictured) would help with the running 'roadshows' in London aimed at attracting troubled youngsters

Anger: Abu Rumaysah (left), formerly known as Siddhartha Dhar, shouts while filming another protest in London in 2011

Taunts: After he was able to 'breeze' out of the UK even though he was on bail he sent a series of tweets taunting the British authorities

It came as it emerged the child in the video is the son of a notorious Jihadi bride from London, according to her own father.

The young boy, dressed in military fatigues and a black bandanna bearing the white mark of ISIS, declares that 'We will kill kuffar [non believers]' in depraved new footage which sees five shackled men in orange jumpsuits brutally murdered by a masked executioner.

The four-year-old boy's own grandfather has now confirmed he is the son of Grace 'Khadijah' Dare, who grew up in Lewisham, south London, to Nigerian Christian parents and converted to Islam as a teenager.

Her father Henry Dare, also known as Sunday, has said that his grandson is 'definitely' the boy in the ISIS video.

Mr Dare, a minicab driver, told the Telegraph: 'I was surprised when I saw the picture. It's definitely him. Of course I'm worried but there's nothing I can do now.

'I'm not angry - I would never have expected it. I just hope someone is trying to bring them back.'

In an interview with Channel 4 news, Mr Dare, who is also known as Sunday, begged his daughter to return to Britain. He said: 'She should come back and face the music. Because, she has let herself down,'

When asked about his grandson Isa, Mr Dare said: 'He doesn't know anything. He's a small boy.They are just using him as a shield.' Mr Dare revealed that he had not spoken to his daughter for 'weeks'.

'When she calls me I keep on ignoring her calls because she has brought shame to my family and to herself,' Mr Dare told Channel 4 News.

This British boy (pictured) who threatened the UK with terror attacks in a sick ISIS execution video is the son of a notorious jihadi bride

This picture of a youngster posing with a toy gun in front of an ISIS flag in 2014 and thought to be Grace 'Khadijah' Dare's son. It was tweeted by Londoner Umm Khattab, the teenaged widow of an ISIS fighter with the caption: 'Next generation, Bi'ithnillah (God willing)'

Her father Henry Dare told Channel 4 News that his grandson is 'definitely' the boy in the sick ISIS video. Mr Dare, who is also known as Sunday, has begged his daughter to return to Britain

In 2014, Dare posted a shocking photograph to her Twitter account of her then four-year-old son Isa, meaning 'Jesus', smiling as he aims an AK-47 rifle.

She is married to a Swedish Islamic fighter called Abu Bakr, and is reported to be a convert who previously attended a mosque in South London.

Isa also has a younger brother, who would now be between two and three years old, who his mother has referred to as a 'mini mujahid', or holy warrior.

The Muslim convert jihadi bride, from South London, featured in a documentary two years ago at her spartan home in the Syrian city of Aleppo after swapping a comfortable life in Britain for the horrors of war.

In the video, published by Channel 4 News, she extolled the virtues of her adopted religion, declaring: 'I'm not oppressed. If I was oppressed I wouldn't be a Muslim right now.

'If I thought Islam was an oppressive religion, I would have left Islam. Islam has made me free.'

She urges other Muslims to 'stop being so selfish... focusing on your families or studies' and implores them to join jihad in Syria.

Her husband, Abu Bakr, is later seen walking into the house with his AK-47 which he lines up with other weapons in the living room and sits down to play with his son's Lego.

As he lays down to rest on a mattress on the floor, he tells how he is heading out that night to fight for ISIS, which paid him just $150 a month to slaughter innocents.

Bakr, a Swede who married Dare after fleeing to Syria in 2012, later died in battle.

At home with the jihadis: British Muslim convert Grace 'Khadijah' Dare appeared in a documentary two years ago with her ISIS fighter husband Abu Bakr and her son Isa in which she boast about her new extremist life

No start in life: The couple's son plays in a rubber ring while they argue about whose machine gun is better

Life of violence and fear: A fully-veiled Dare and her neighbour head to the shops with their children to buy 'hummus, nappies and a bucket' while carrying Kalashnikovs over their shoulders in case of emergencies

'Sid' Dhar had publicly stated that he wanted to live under the Islamic State in Syria.

Speaking from his Walthamstow home, a former neighbour who did not want to be identified, said he knew something was wrong when he saw Dhar on TV protesting against British soldiers returning from tours of the Middle East.

He said: 'I think he is a scumbag. We first new that he was a wrong'un when we saw him on TV when British soldiers were returning. That was not even a year after we moved in.

'At first he seemed quite normal. They took in parcels for most people on the street.

'One day I was just throwing my rubbish away and I found all these flyers in the bin that said 'Muslims against Crusades' and talked about Sharia Law in Waltham Forest.

'They tried to say that it was a peaceful organisation but we knew it wasn't. He was one of the people burning poppies and in Whitechapel telling women to cover up and gay people not to be gay.'

'He never worked. He used to come by occasionally with a van full of bouncy castle equipment but we always thought it was a ploy,' the neighbour claimed.

'There were really dodgy characters that would come to the house. All men in religious dress just hanging around looking a bit suspect.

'When the council came to sort out the house for the new tenant they found the cellar was full of the flyers and temporary cots that had gone mouldy.

In a 2013 interview with Vice News, he also talked about his conversion after 9/11 and described David Cameron and MPs as 'the real preachers of hate and violence... who are allowing soldiers to fire bullets of extremism at men women and children in Afghanistan.'

He told the website: 'We believe that whenever the sharia is established, the pure Islamic state maybe in Iraq or Syria, one day the leader will wage jihad and annexe Britain into the Islamic state.

'We are not going to forget Europe, we are not going to forget Britain, the armies will be sent here to conquer these lands.'

Fanatic: Dhar speaks about ISIS in a documentary by English-language Islamic TV channel Ahlulbayt in 2014

ISIS also threatened David Cameron in the video in which it executes five suspected spies (pictured)

The terror group's captives (pictured), dressed in orange jumpsuits, were filmed 'confessing' in Arabic to spying for British security service

The chief executioner (pictured) in ISIS's newest propaganda video wore military fatigues and spoke in a clear British accent

A few weeks before his arrest, he told one interviewer that he was willing to renounce his British citizenship if it meant he was allowed to travel.

But his family say they are unsure if it's him in the new ISIS execution video and maintain he was a 'sensitive' person.

His sister said: 'He was a very pleasant boy, and I know it may be hard to believe but he still is, and I still believe that he still can be that person.

'I definitely know him as a good person, no doubt about that.'

His mother also defended his character as a child, saying: 'He was sensitive, very sensitive. He was shy, very shy. And that's who I know. This is why it's very difficult for me at this time.'

In the footage released over the weekend, the five captives were forced to confess to their crimes - most probably under duress - before they were paraded to a remote desert location and ordered to kneel.

The English speaking jihadi, believed to be Dhar, yelled 'Allahu Akbar' before he and four other fanatics shot the men from point blank range.

The video ended with a trailer for another execution in which a young, dark skinned boy warned Britain of coming atrocities.

It raised fears that the child, who appeared to be around five, may have been made to execute someone on camera.

Before killing the prisoners in cold blood, the British jihadi said: 'This is a message to David Cameron, slave of the White House, mule of the Jews.'

He called the Prime Minister an 'imbecile' and warned 'your children will pay' for British airstrikes on ISIS targets in Syria.

The masked executioner in the video bore a chilling resemblance to ISIS's former executioner in chief, Jihadi John.

The fanatic, real name Mohammed Emwazi, was filmed executing British aid workers David Haines and Alan Henning, American journalists Steven Sotloff and James Foley, American aid worker Peter Kassig and Japanese journalist Kenji Goto.

He was killed by a US drone strike near an iconic clock tower in the terror group's de facto capital of Raqqa in Syria in November.

Security experts believe the mass execution is the culmination of an Islamic State manhunt for those who helped Western forces kill Emwazi.

Among the five men shot dead are understood to be those suspected of providing information on his movements and appearance.

The victims give their names and briefly discuss the details of their so-called offences – presumably under duress. Although their identities could not be verified, among them was Umaar Hamud al-Ja'far, 30, from Raqqa, who said he supplied information about the city's topography. Another victim, Ubi Muhammad Abdul Ghani, 26, said he undertook covert surveillance.

Faisal Hamud al-Ja'far, 25, said he was also from Raqqa and stated he was paid money to open an internet café in the city.

Mahyar Mahmud al-Uthmaan, 31, says he accepted a payment of $300 in Turkey, also to open an internet café. Ha'il Marwan Abdul Razaq, 40, admitted taking pictures of militant activity.

Intelligence agencies are already working to identify the young boy and the older British jihadi in the film.

More than 800 Britons have travelled to Syria and Iraq to fight for Islamic State, including families from Luton, Bradford and London.

The new video, which featured a child threatening Britain, comes a month since RAF jets began bombing ISIS targets in Syria.