Carrying billowing black flags, Anjem Choudary's banned group of extremists stomped past the Lebanese cafes and phone accessories shops along north London's Edgware Road, just weeks before the brutal killing of a British soldier Lee Rigby on the other side of the city.

The cleric's ragged band of foaming-mouthed supporters has pounded British pavements for years, but this time, the protest was different. It wasn't a picket of Remembrance Day, or a complaint about cartoons.

The target was other Muslims.

anjem choudary

Anjem Choudary led the first Muslim sectarian protest on British streets

On the surface, it was a demonstration in support of the rebels in Syria. In reality, the objective was to intimidate members of the minority Shia Muslim community in the UK, Muslims whom followers of Choudary's brand of extreme Salafist Sunni Islam do not consider true believers.

Activists carried banners rallying against the "Shia Enemies of Allah" and police had to be called to the scene when members of the group apparently attacked a man who was Shia, hitting him almost a dozen times.

The demonstration is the first time that bitter Muslim sectarian tensions, now one of the driving forces behind the war in Syria, have bubbled to the surface, leading to violence on the streets of London.

But experts say that Sunni-Shia divisions have long been creeping beyond the borders of Syria and, for that matter, Iraq, and into mosques and onto university campuses in the UK.

Communities leaders are concerned about tensions escalating as the Syria conflict deepens, and the Muslim Council of Britain, a coalition of Muslim organisations across the theological spectrum, issued a strongly worded statement condemning the Choudary protest.

Farooq Murad, secretary general of the MCB, told HuffPost UK the Choudary protest was an "unhappy episode".

This weekend, the MCB published an intra-faith unity statement, aimed at tackling the problem, signed by leaders from both the Sunni and Shia traditions of Islam.

The MCB calls the statement a "signal to the British Muslim community and to the world that we will not allow hatred and division to be preached by our brothers and sisters in Islam towards our brothers and sisters in Islam."

"There's no point in denying the fact that [overseas conflicts] may have consequences here, and in Syria there is certainly a sectarian dimension," Murad told HuffPost UK.

"Certainly conflicts can spill out to create more general sectarian tensions and divides. They exist anyway, and it heightens those fault lines."

According to Liverpool University academic Leon Moosavi, British Muslims have been mostly been concerned over the past decades dealing with Islamophobia, and debating the war on terror, Israel and Palestine.

"These used to be issues which Muslims united around, regardless of Shia or Sunni affiliation. But these unifying issues are disappearing.

"Muslims are now debating and talking about the Arab Spring, Syria, Turkey. This is what is shaping people's identities now.

"There has always been a division, but the problem is that it is so pronounced at the moment, the Syria conflict has forced people to their side of the spectrum, people are feeling their sectarian identity really matters."

Fiyaz Mughal, the Sunni founder of Tell Mama, which monitors Islamophobia and inter-Muslim hatred, told HuffPost UK that the killings of Sunnis by Assad forces and Lebanon's Hezbollah "feed a mental divide that is not widespread, though which plays at the back of the minds of mainly Arab communities in the UK”.

Mughal added: "It is also being used by those who want to drive a wedge between Sunnis and Shias and whilst they are in the tiny minority, they are vocal.”

shia sunni

An Iranian demonstrator tears up a portrait of Saudi King Abdullah bin Abdul Aziz during a protest in front of the Saudi embassy in Tehran

Sunni and Shia Islam are the two major denominations. Between 80-90% of the world's Muslims are Sunni, according to research by the Pew Forum in 2009. Those percentages are generally believed to be reflected in British demographics.

Sunnis are the majority in most Muslim countries around the world; Shias are believed to be the majority only in Iran, Iraq, Azerbaijan, and Bahrain.

"The Islamic community in Britain has only really had a consciousness of itself in the last 30 years," Moosavi explained. "Back then, the community was far more united, Muslims stuck together, Shia and Sunni Muslims used the same mosques back in the 1980s.

"After the Second Gulf War, after 9/11, that was a massive turning point for Shia-Sunni division. It's emerged now in Bahrain and obviously in Syria.

"And it does play a role in Muslim relations in the UK because we live in this globalised world where what happens over there affects what happens here. People move backwards and forwards all the time."

The division, which centres on the schism that occurred after the death of the Prophet Muhammad in 632 over who would be his successor, has influenced conflicts across the world, most recently in Pakistan, Yemen and Bahrain.

The 2003 war in Iraq was the turning point for Shia-Sunni division globally, as Iraq descended into civil war, but protests and violence in Bahrain and Syria have put the issue front and centre in the Middle East. In Syria, President Assad is an Alawite Muslim, which is an offshoot of a Shia Islam.

But the majority of Syrians, and the official Syrian opposition groups, are Sunni.

Egypt's most senior Muslim cleric, Grand Sheikh Ahmed al-Tayeb, a leading voice of mainstream Sunni Islam has condemned Shi'ites for engaging in "hateful sectarian strife" in Syria, according to Reuters, calling the violence a "theatre of the absurd in this battle which has become a Shi'ite-Sunni struggle."

Violent sectarian attacks have not only occurred in Syria. Four Egyptian Shia Muslims were killed in a mob attack in a village near the capital Cairo, officials say. The attackers accused those gathered of trying to spread Shia beliefs, according to the BBC.

The sectarian nature of the struggle in Syria is fuelled by the puritanical and fundamentalist Salafi movement of Sunni Muslims, which became a force in Syria's civil war and across the region in the wake of the Arab Spring.

sectarian syria

Anti-Syrian regime protesters hold a banner in Arabic that reads: "The sectarian storm cannot be extinguished without eradicating those who spark it," during a demonstration, at Hass town, Idlib province, northern Syria

Salafi militants Jabhat al-Nusra are recognised Al-Qaeda affiliate, but other Salafi networks are operating across the country.

And militant Lebanese Shi'ite group, Hizbollah, has mobilised fighters to help Assad. Salman Shaikh, director of the Brookings Institution’s Doha Center in Qatar told Reuters that without Hizbollah's involvement, the struggle “would have been more of an inter-Syrian fight rather than being a sectarian one."

And because of the new colour the conflict has taken on, British Muslims are being called on to take sides, along sectarian lines.

"The conflict there has taken on an increasing sectarian dimension," Shiraz Maher, an extremism expert at Kings College London told HuffPost UK.

"It's not been widely reported, but the Assad forces, when they capture rebels, they make them say a version of the Muslim testament of faith 'there is no god, but god'. But instead they make them say 'there is no god, but Bashar al-Assad'.

"And that, in conservative Sunni Muslim circles, makes people think that this about Assad wanting to kill Sunni Muslims, he wants to wipe us out."

The MCB's Murad, who is a Sunni Muslim, admitted community leaders were worried "whenever there's conflict abroad in Muslim countries" and had discussed creating a code of conduct for mosques with regard to sectarian hate preaching.

Murad said that he does expect more marches and demonstrations in support of Syrian causes, "there's a sizeable community here of Syrians. And it can mean that some will try and turn those demonstrations into a sectarian issue. But we can't allow them to succeed. It is not about that."

But few that we spoke to believe that such protests will become a common occurrence.

"The Syria opposition based here wants to present itself as reasonable and responsible," Maher told HuffPost UK.

"They won't be organising any sectarian protests. And they are very acutely aware of not getting involved in sectarianism."

High-profile British Iraqi Shia lecturer Sayed Ammar Nakshawani said that the protests made no sense to the ordinary Muslims. "These guys calling for Sharia law and marching up the Edgware Road are going to cause havoc whatever happens.

"Syria is just an excuse for them. Those who use Assad to attack Shias in this country, you say to them, why not speak out against Saudi and Qatar? Saudi is the least democratic country on Earth."

sectarian syria

Syrian workers clean broken glass inside the Sayyida Zeinab shrine after a car bomb exploded near the shrine, in a suburb of Damascus

Liverpool University's Moosavi said that in the age of the internet, divisions manifest in different ways.

"It is not common to protest about it, the younger generation express hatred via the internet, social media, describing each other as non-believers. I came across on YouTube a rap which criticises the other sect of Islam.

"It appears on university campuses, in Islamic societies, in prayer rooms, which can turn into places of conflict. It would also be wrong to say this is just a Sunni-Shia divide, there are divisions in Sunni Islam too."

Muslim leaders and experts on the community told HuffPost UK that tension was being fuelled not only by the Syrian conflict, but also by satellite broadcasts of preachers from the Middle East, and preachers from abroad coming to speak in British mosques.

Two have caused particular concern, the arrival of Shia preacher Yasser Al-Habib, to open a mosque in Buckinghamshire, and the visit of Saudi Mohammad Al-Arefe, a Sunni cleric in the last week.

Al-Habib was imprisoned in his home country of Kuwait in 2003 for inciting sectarianism, but denies that he hates Sunni Muslims. Al-Arefe, who is currently doing a tour of the UK, is accused of a similar hatred of Shias.

A leading British Shia institution, the Al-Khoei Foundation has warned of the damage both preachers could cause. Yousef Al-Khoei, director of the institution, told HuffPostUK: "We have had a very cordial relationship for many years between Sunni and Shia Muslims. But preachers come from abroad, and try to stir it [division] up.

"He [Al-Arefe] has been very vocal in trying to create these divisions. But we will work to make sure these guys don't win."

"He has said he is on a mission, a jihad, at a lecture in Egypt. And we expect him to say this, and expect that his very presence on British land to be controversial."

The same concern has also been voiced by Tell Mama, and Labour MP Khalid Mahmood, who has said both were in the UK "purely here to promote themselves and create divisions where none need to exist."

Al-Arefe told HuffPost UK on Friday that it was "nonsense" to suggest he was here to whip up tension.

"To be completely clear, I advise both Sunni and Shia’ in the UK to continue to respect one another despite what is going on in Syria.

"I would invite and welcome the opportunity for open and frank discussions with members of any sect or faith, whom I am sure, regardless of their beliefs, are deeply moved and concerned about the suffering inflicted on the Syrian population daily by a cruel regime and its supporters."

Some disagree that division is only spread by those coming from outside the UK. "I think the sectarianism is not just caused by outside preachers, but also those born and raised here," Moosavi said.

"Muslims who were born and raised in European countries are travelling to fight in Syria, usually with the rebels, because of how increasingly sectarian the conflict has become."

Those who would create division are usually a "minority of hardcore Salafists who regard Shias as non-Muslims," Maher added. "It is exaggerated by what happens in Syria. But the idea of a Salafi imam coming over and saying derogatory things about Sunnis has happened before and will happen after Syria."