Police forces across the world are prepped for Eritrea’s independence day this Friday - fearing violent clashes as disgruntled Eritreans unable to protest at home may do so at events abroad to mark the day 33 years ago that the country was born. Some countries have even banned the celebrations.

It was a hard-won battle to gain freedom from Ethiopia - coming after a three-decade conflict. But the anniversary is bittersweet for some as the promised freedoms have never materialised.

President Isaias Afwerki has ruled Eritrea for the last 33 years without holding a national election.

It is the only country in the world that does not have a constitution. Any form of political dissent and association outside that of the ruling PFDJ movement is not allowed.

There has been no free press since the closure of independent newspapers and arrest of most of their editors and journalists in 2001.

Hundreds of thousands of young Eritreans have escaped to the diaspora, many taking dangerous journeys to flee the indefinite military conscription that is the fate of any able-bodied citizen.

Through this mandatory national service, Eritrea has become one of the most militarised societies in the world.

It is from this pool of Eritrean migrants that a new form of opposition has formed in the diaspora - with a much more radical edge to it.

They are fed up with fragmented exiled opposition groups, made up, among others, of disillusioned former senior leaders of the government and PFDJ.

Determined to fight against the regime they believe forced them out of their country, they formed a militant youth group, known as Brigade Ni’hamedu, two years ago.

Their battleground is pro-government national anniversaries and festivals organised by embassies and pro-government communities.

Given Eritrea’s history there is a big mix of communities abroad - including people who left during the war, sending home money to support those who were fighting and who are still proud that their efforts saw the creation of a new nation.

For a long time, opposition activists in exile say they have been harassed and intimidated by the PFDJ even in countries where they have sought refuge.

Robel Asmelash, chairman of Brigade Ni’hamedu’s UK chapter, says his contemporaries feel it is time to fight back.

“The people have been denied the right to express its opposition peacefully,” the 27-year-old taxi driver, who fled military service in 2013, told the BBC.

Their campaign also goes by the name the “Blue Revolution” - a reference to the blue flag created in 1952 when British-administered Eritrea became an autonomous region of Ethiopia before it was later annexed.

It has branches across the world and insists any pro-government event should not take be allowed to take place.

Over the last year, Canada, Germany, Israel, the Netherlands, Sweden, Switzerland, the UK and the US have all witnessed violent confrontations at these gatherings.

The two rival groups have used stones, sticks and in some instances knives to assault each other.

In Tel Aviv the tension has escalated into tit-for-tat attacks and a few weeks ago a Blue Revolution activist was killed, leaving four children and a wife behind.

A pro-government supporter is reportedly fighting for his life in hospital after he was seriously hurt on the same day.

Last week, police in London released photos of Eritreans wanted for their involvement in an attack in December, when they stormed a pro-government event taking place at a theatre in Camberwell and injured several officers.

“The level of violence used against officers, who were there to keep the public safe and protect people in a theatre, is some of the worst I have seen,” said a detective investigating the matter.

“We have so far arrested 44 people for a number of offences relating to this demonstration and continue to make progress, however, there are still outstanding a number of suspects that we need the public’s help to identify.”

The Blue Revolution's action is having some effect, as the Swiss authorities have refused permission for this year’s national day celebrations to take place.

Eritrea's embassy in Switzerland said it was appalled, accusing the authorities of appeasing “violent thugs”.

The Dutch city of Rijswijk has also banned the independence day gatherings.

Mr Robel admits that things may have initially got out of hand at some events, but says that Brigade Ni’hamedu members have also been targeted.

“In the beginning, there was no leadership that would manage things and take safety responsibly - as a result many of our members became victims of violence,” he said.

“But now in all countries, leaders of Brigade Ni’hamedu are providing awareness about protest laws.

“In co-ordination with law enforcement forces, we shall continue our resistance.”

This is because he is aware that it is not only his contemporaries who have been radicalised.

A generation of Eritreans born in the diaspora, whose families are more aligned to the government, have also been mobilised.

The ruling PFDJ has set up a youth wing for the diaspora, described by one of its officials as a “militant” group.

Set up in 2005, the Young People’s Front for Democracy and Justice (YPFDJ) was created to expose “the lies spread by the enemies of Eritrea”, according to the state-owned news site.

Some of those recruited have even travelled to Eritrea to take part in military training at the notorious Sawa Training Camp - though unlike conscripts born in Eritrea, they can leave.

In fact, President Isaias, who has never ended his country's war footing, introduced a new system of governance in 2017, known as the “Four Defiance Fronts”:

• The first three fronts - Eastern, Central and Western - operate in the country and include the army commands in their respective regions

• The Fourth Front, referred to as 4G thanks to its Tigrinya acronym, is organised and mobilised by Eritrean embassies and the zealous YPFDJ branches abroad.

Daniel Teklai, an Eritrean based in California in the US who describes himself as a nationalist rather than PFDJ supporter, told the BBC this envisaged the diaspora as an “economic zone”.

The 53-year-old banking professional says it is wrong to see the many Eritreans in the diaspora who send back remittances in the spirit of patriotism as having blind allegiance to the PFDJ.

Mr Daniel has spoken out against the government in the past, but says his patriotic fervour was revived during the recent two-year war in Tigray, the northern province of Ethiopia, which is on Eritrea’s border.

Eritrea fought in the conflict on the side of the Ethiopian army against fighters of the TPLF, a party that once ruled Ethiopia and is blamed by its neighbour for their deadly 1998-2000 border war.

“During the conflict, the vast majority of Eritreans abroad, regardless of their political views, rallied behind Eritrea's government, its armed forces, and the nation's interests,” Mr Daniel explains.

“This show of unity led to a surge in the popularity of independence day and other national holidays, with celebrations becoming even more vibrant and patriotic.”

However, the vast majority of Blue Revolution supporters, many of whom fled conscription, were opposed to Eritrea’s involvement in the Tigray war.

“In response to this surge in national unity, a radical fringe of the opposition resorted to violence... throwing stones, burning cars, damaging property, and assaulting police officers,” says Mr Daniel.

He does not believe that the YPFDJ has ever been associated with any counter-violence, putting the blame firmly on their rivals.

As the co-founder and chairman of One Nation, an organisation that advocates democratic change in Eritrea, he is determined to see Eritrean festivals worldwide thrive - and does not see cancellation of the jamborees as an answer to the actions of “extremists”.

“The solution is not to surrender to these tactics. Law and order must prevail.

“Those who break the law by committing these crimes must be held accountable for their actions.”