They were friends enjoying an evening out in a city transformed since the Troubles, unwittingly close to losing their lives at the hands of extremists still wedded to the past.

Soon after they passed, the pizza delivery vehicle exploded, engulfing the pavement in a ball of flames.

“It was only by good grace that local people weren’t killed,” said PSNI Assistant Chief Constable Mark Hamilton as he laid the blame squarely on the New IRA.

“This was a callous act against the people of Derry.”

The dramatic CCTV footage of Saturday night’s car bomb has served as stark reminder of a time the people of the North hoped had been left long behind.

It has also raised uncomfortable questions about dissident republicanism and the threat it still poses, 21 years on from the Good Friday Agreement.

A cloud of uncertainty has hung over the Maiden City all week, with residents wondering if it was an isolated act of defiance to mark a date in history or a sinister portent of a more worrying future.

Concerns merely intensified on Monday with the sight of masked men hijacking vehicles in broad daylight as three bomb alerts, all subsequently declared hoaxes, caused widespread disruption.

The New IRA is a title its members dislike. They instead style themselves simply the IRA, laying claim as the true inheritors of those who fought British rule in the War of Independence.

One hundred years on from the inaugural Dáil sitting in the Mansion House and the war’s first shots at Soloheadbeg in Co Tipperary, the dissidents appeared to be sending a blunt message that their war is still not over.

The New IRA is the biggest dissident republican organisation on the island, having formed seven years ago from the remnants of the Real IRA — the group behind the 1998 Omagh bomb — and several other disparate anti-peace process factions.

There is also the Continuity IRA, whose origins date back to a 1986 split with the Provisional IRA, and Oglaigh na hÉireann (ONH), which declared a ceasefire in January last year.

An ONH splinter group opposed to the decision to pursue peaceful means subsequently announced it would continue its armed conflict as the Irish Republican Movement.

Another dissident grouping that has recently emerged is Arm na Poblacht.

Collectively the number of active dissidents is thought to be in the low hundreds. They comprise both hard-line veteran republicans who left the Provisionals behind when they renounced violence and younger recruits with no memory of the bloody sectarian strife of the Troubles.

Members are drawn from both north and south.

They come nowhere close to the size or capability of the PIRA, nor do they attract anything like the community support the Provos enjoyed during the 30-year conflict.

But they remain extremely dangerous nonetheless, particularly in the areas where they are strongest: Derry, north and west Belfast, Strabane in Co Tyrone, Lurgan in Co Armagh, and pockets of Tyrone.

While they have proved themselves incapable of mounting a sustained campaign of violence, they continue to demonstrate the ability to launch sporadic and sometimes deadly attacks.

In the last 10 years, dissidents have murdered two soldiers, two police men, and two prison officers.

British army sappers Mark Quinsey and Patrick Azimkar were gunned down by the Real IRA as they collected a pizza delivery outside Massareene army barracks in Co Antrim in March 2009.

Two days later PSNI constable Stephen Carroll was shot dead by the Continuity IRA in Craigavon, Co Armagh.

In April 2011, freshly qualified PSNI officer Ronan Kerr was killed by an undercar booby trap bomb outside his home in Omagh, Co Tyrone.

In November the following year, prison officer David Black was shot dead as he drove to work along the M1 motorway in Co Armagh.

In March 2016, fellow prison officer Adrian Ismay died from injuries sustained in a car bomb attack in east Belfast.

The latter three murders have been linked either to the New IRA or individuals now thought to occupy its ranks.

The group has also been responsible for several other serious terrorist incidents, including the shooting and wounding of a policeman on a busy petrol station forecourt in north Belfast in January 2017.

But, prior to last Saturday, there had been evidence the New IRA, and the other dissident groupings, were becoming less active.

There was only one recorded national security attack in the North last year, compared with five in 2017, four in 2016, and 16 in 2015.

There were 17 bombing incidents in 2018, compared to 29 the year before.

Army bomb disposal experts still attend regular call outs across the region, but their workload has dropped and, as Monday demonstrated, many alerts transpire to be elaborate hoaxes.

In a bizarre incident last summer an infuriated motorist in Belfast got out of his car, picked up the suspect device blocking his path — a gas canister with some wires taped to the side — brought it home, and turned it into a wood burning stove, posting the whole episode on social media.

His actions, ill-advised as they were, were an extreme example of a growing sense of apathy among us toward security alerts, with commonplace scares increasingly met by community frustration rather than fear.

Shootings linked to the security situation have decreased too — 39 last year compared to 58 in 2017.

The longer-term trends also indicate a steady fall in paramilitary use of the bullet and bomb. In 2010 there were 79 shootings and in 2011 there were 99 bombing incidents.

Last year 17 people were shot in paramilitary-style vigilante attacks in Northern Ireland, compared to 28 in the previous 12 months.

Though these statistics all point to a gradual deterioration of dissident capacity and intent, they do not tell the full story.

What is not captured by the figures is the increasingly successful efforts of the PSNI, MI5, and An Garda Síochána in thwarting many other acts of violence.

Recent cases north of the border have revealed the extent of sophisticated surveillance techniques being deployed, suggesting many of the main players are on constant watch.

Fears of infiltration have also sparked internal rows among the disparate groups, leading to further splits and undoubtedly instilling a hesitancy among some wavering recruits to get involved.

SINCE 2011, the British government has given the PSNI around £400m additional ring-fenced funding to resource counter-terrorism work. The operational deployment of the National Crime Agency, the UK’s equivalent of the FBI, has also bolstered efforts to clamp down on organised crime rackets run by paramilitaries.

Gardaí have achieved significant success south of the border as well, with intelligence-led operations resulting in significant seizures and interceptions. Police in the North rate the working relationship with the Garda as the best it has ever been.

So, while the official figures record fewer violent incidents, there is little doubt the numbers would be significantly higher but for the relentless work of the authorities.

Police commanders are certainly not complacent enough to think the dissidents have had their day.

Vigilance is key and, as Saturday showed, they only need to slip through the net once to make a potentially devastating impact.

The threat level in the North remains classified as severe, meaning further attacks are highly likely.

And that ever-present menace of violence is corrosive.

It has been cited as a main factor holding back efforts to address the religious imbalance within the PSNI.

Catholics are not applying in the same numbers as Protestants due to fear of reprisals for them or their families.

Dissidents have actively targeted Catholic officers in the past — Constable Kerr’s murder being a stark example — to create a chill factor and stymie PSNI efforts to build trust in once hostile nationalist communities.

One Catholic from Derry who did join the ranks of the PSNI recently told the BBC he had been forced to cut all ties with his family as a result.

“Once you join up as someone from Derry it is very hard to socialise with your family, or come back into the city,” he said.

Such instances prove the dissidents do not need to be large in number to exert a pernicious influence.

Commanders in Derry have been on high alert for several weeks now, concerned at an apparent step-change in dissident activity and reports of intensified recruiting efforts. Intelligence has painted a similar picture in Belfast.

It is against that backdrop that detectives are investigating the courthouse bombing and trying to establish what might come next.

Britain’s Northern secretary Karen Bradley was at pains this week to reject any notion the violence was linked to Brexit.

“The attack on Saturday night is the result of a threat level that has been in place since before the Brexit vote,” she told MPs in the House of Commons.

“Those people have been working and trying to carry out these plots and activities for many years.”

Derry, while close to the border, has been the focus of dissident activity for years and, if this week’s activities were meant to send a message about Brexit, that was not apparent from the target.

Bishop St courthouse, a heavily fortified symbol of British rule adjacent to the nationalist Bogside, has been attacked by republicans in the past, but it is hardly redolent of the Brexit impasse.

The incident was more likely timed to coincide with the centenary of the Soloheadbeg ambush and the first Dáil.

Minutes after the bombing on Saturday, republican socialist party Saoradh was quick to reference events in Co Tipperary 100 years previously in a tweet that also used the hashtag #Dail100.

While Saoradh denies any link with the New IRA, a claim the police dispute, it certainly would be in tune with its thinking.

Even if Brexit was incidental to the latest events in Derry, there remains concern among senior officers on both sides of the border that the thorny issue could spark a further upsurge in dissident activity in the months ahead.

Not that dissident republicans are any defenders of the European Union — quite the opposite, ideologically they view the institution as a capitalist super-state intent on usurping Irish sovereignty.

Instead there are fears they may attempt to exploit the renewed political focus on the border, at home and internationally, for their own ends.

To the extremists, the return of any physical border infrastructure would be manifestation of the inequities of partition.

The Police Federation for Northern Ireland, the body that represents the rank and file of the PSNI, has warned that checkpoints would be seen by the dissidents as “propaganda gifts” and “sitting ducks” for attack.

MORE than a century on from the First World War and physical force republicans are hoping England’s difficulty could again bring their opportunity. But the dissident battle is as much for the heart of republicanism as it is with the British state.

In republican communities in Belfast and Derry they are a thorn in Sinn Féin’s side, trying to undermine and challenge the party’s long-held pre-eminence. Sinn Féin offices have been attacked on several occasions in recent months and, last July, crude industrial fireworks were thrown at the Belfast homes of Gerry Adams and veteran republican Bobby Storey.

Sinn Féin was quick to blame dissident elements, with Mary Lou McDonald branding them “enemies of the people”.

In Derry, the death of Martin McGuinness, a totemic figure within republican circles, has left the party shorn of one of its most powerful community influencers, a persuasive voice in countering the dissident narrative.

At the ballot box, dissidents have failed to make any sort of a dent in the Sinn Féin vote, a pattern that is unlikely to change.

But they are a problem for the party nonetheless, especially when it comes to wielding influence on vulnerable young people.

In Derry last summer, rioting fomented by dissidents saw youths embroiled in disorder in the Bogside for six successive nights.

At the height of the unrest, dissidents used the disturbances to launch murder bids on police, shooting an automatic weapon and throwing explosives at officers stationed on the historic city walls.

Similar tactics have been used in Lurgan in recent years, with rioting whipped up to lure police toward danger.

There are concerns that ability to orchestrate street violence may factor amid the turbulence a chaotic Brexit might bring.

In that context the political vacuum at Stormont is not helpful.

Politically, dissidents view the collapse of powersharing as proof the Good Friday Agreement is a busted flush and Sinn Féin’s historic decision to sign up to a partitionist deal was not only a grand betrayal, but also a grand folly.

Practically, there have also been consequences of not having a functioning government for two years.

An ambitious Stormont strategy to tackle the root causes of paramilitarism has stalled, while a law that would give police more power to seize the ill-gotten gains of suspected terror bosses remains unenacted.

Inaction on wider socio-economic issues must also be considered.

Hardliners thrive in areas of deprivation and underinvestment, places where the dividend of peace is sometimes difficult to identify, and the current political impasse is limiting statutory efforts to tackle those problems.

The scourge of paramilitarism continues to hold back many working-class communities across the North.

Republican and loyalist gunmen alike rake in millions every year through racketeering and while so-called punishment shootings and assaults are decreasing, they still happen all too often.

Aside from politically motivated killings, dissidents and loyalists have been responsible for multiple murders within their own communities in recent years, crimes not widely reported outside of the North as they are not seen as significant challenges to national security.

The head of peace-building charity Co-operation Ireland provoked debate last year when he called on people to stop using the word paramilitary.

For Peter Sheridan, a former police commander in Derry, it bestows a measure of legitimacy on groups he suggests are now simply crime gangs that pay only lip service to political ideals.

“It is about turf wars, it is about internal feuding, it is about ordinary criminality; it is nothing to do with the conflict that they are involved in,” he said.

“Yet we continue to separate out these two things as if they are somehow different.

“We need to re-brand Northern Ireland, we are the only community that I know of that talks about paramilitary organised crime as if they are somehow separate.

“Post-1998 and the Good Friday Agreement, thereafter people are, in my view, in organised crime gangs.”

New IRA or IRA, paramilitary or criminal — whatever you call them, the events in Derry suggest the dissidents are not intending to leave the stage anytime soon.