A fireball outside a courthouse. Hijackings and bomb alerts. Sealed-off streets, evacuations and arrests. Speculation about the next attack.

It can seem as if Derry has stepped into a time machine. Television pictures in the past few days have shown images redolent of the Troubles, an era supposedly consigned to the city’s museums and murals.

Ice and snow blanketed the scorch marks outside the Bishop Street courthouse on Tuesday as police with body armour and rifles patrolled the streets and continued to hunt the dissident republicans blamed for 72 hours of chaos – a car bomb on Saturday was followed by groups of masked men mounting three separate van hijackings, triggering widespread bomb alerts.

CCTV footage showed young people strolling past the rigged vehicle minutes before it exploded on Saturday. Police called the bomb crude, unstable and incredibly reckless.

There were no casualties, but the blast and its aftermath in Northern Ireland’s second city provided a dramatic counterpoint to the febrile political mood in Westminster and across the UK. Could the Troubles be returning?

On the streets of Derry the answer is no.

The New IRA, the group believed to be responsible for the incidents, has negligible support and limited capacity, and is a feeble, unwanted, wannabe successor to the Provisional IRA, say residents.

But the last few days have been unsettling nonetheless. As Lisa McGee, the creator of the TV series Derry Girls, tweeted: “What the HELL is going on?”

It is a common question. People are angry and in many cases scornful about the bombers – but there is a tinge of fear. Five men arrested in connection with the bomb have been released.

“The Troubles are finished. This is just a criminal element in the town that no one wants,” said Kathy Browne, 53.

“It’s a disgrace,” said Martina Houston, 30, who lives with her six-year-old daughter, Brooke, close to the courthouse. “My wee one heard the explosion. We had to let her sleep on the sofa that night and carry her to bed when she was asleep.”

A controlled explosion by army technicians on one of the hijacked vans on Monday frightened the girl again, said Houston. “She was squeaking her heart out. She would not leave the house.”

Houston, born in 1988, barely remembers the Troubles and does not want a sequel. “They’re trying to bring it back to the way it was. You don’t know what this town has come to these days, you wonder are you safe.”

Martina Houston and her daughter, Brooke. Photograph: Paul Mcerlane/The Guardian

Some residents wondered if they would need to relearn rusty reflexes – avoiding courthouses, police vehicles and other potential targets – and teach them to a generation that did not grow up with checkpoints and the drone of army helicopters.

“When the young ones were told to evacuate on Saturday they went out to the street and took pictures, they didn’t understand the danger,” said Violet Atkinson, who is in her 60s. “The older ones, we know.”

Residents of a certain age remember what bombs and bullets can do, said Elaine Doherty, 55, a psychologist. “It’s not something that you’re boasting about.”

A resident in his 50s, who declined to be named – “it’s not 100% healthy, there could be repercussions” – said the past few days were mild compared with the 1980s but left an ominous feeling. “It puts a 1% fear in your head: my God, is this coming back?”

Colum Eastwood, the leader of the Social Democratic and Labour party (SDLP), said the New IRA could not mount a sustained campaign.

“For that they need a certain level of support in the community and they don’t have that. It’s not comparable to what went on in the past. People are angry that such a small number of people can cause such chaos and tarnish the reputation that we’re trying to build up as a tourist destination and a city that is moving forward.”

There was a caveat. Dissident republicans have tried in vain to reignite conflict since the 1998 Good Friday agreement – but now they can operate in a vacuum created by Brexit and the collapse of the power-sharing executive at Stormont in 2017.

“We’ve been able to starve them of political relevance for 20 years,” said Eastwood. “Now they’re able to cling to the chaos and worry that’s out there because of Brexit and the lack of an assembly.”

Karen Bradley, the Northern Ireland secretary, has said the bomb had “absolutely nothing to do with Brexit”. Nigel Dodds, the Democratic Unionist party’s leader in Westminster, echoed that.

The New IRA emerged in 2012 via a merger of several groups opposed to the peace process, including the Real IRA. It has been linked with the murder of two prison officers and multiple other attacks, many pre-dating Brexit and talk of a hard border.

The Bogside area of Derry. ‘People are afraid to come out,’ one resident of the city said. Photograph: Paul Mcerlane/The Guardian

They number just a few hundred, not all active, and can stage only sporadic attacks with limited firepower, say analysts.

Saoradh, a fringe political party linked to the group, credited Saturday’s bomb to “republican revolutionaries” taking on “crown forces” and linked it to this week’s centenary of Ireland’s war of independence.

The language, like the attack, seemed anachronistic. But dissident republicans think Brexit has gifted them their best opportunity since the 1916 Easter Rising, said Marisa McGlinchey, the author of a forthcoming book, Unfinished Business: The Politics of ‘Dissident’ Irish Republicanism.

If so Tuesday’s headlines provided more succour: the European commission said a no-deal exit would result in a hard border. And the business group CBI warned no deal could leave Northern Ireland’s economy almost £5bn less productive by 2034.

Future historians may mull the irony of English nationalism stoking radical Irish nationalism, but people in Derry on Tuesday were busier worrying about the next security alert.

Merwan Aytas, who runs a barbershop near the courthouse, gestured to his near-empty shop. “People are afraid to come out. I hope this doesn’t continue. People don’t want this happening again.”