Fittingly for a place that deals in death, the town of Kazanlak does not advertise its wares. Sprawling across a rose-covered valley in central Bulgaria, it looks like any other stretch of the Iron Curtain rust belt, a huddle of drab tower blocks and derelict factories. In the tourist kiosk in the main square, visitors learn that its main claim to fame is as a rose oil producer, with an annual flower festival and a Princess of the Roses beauty contest.

The real money in Kazanlak, though, comes from the rather less fragrant trade that takes place behind the razor-wired walls of a factory outside town. In Soviet times, the Friedrich Engels Machine Building Plant was officially a car factory, churning out a squat saloon that was Bulgaria’s answer to the Trabant. In fact, its 20,000 workers made a far more successful Soviet export – the Kalashnikov AK-47 assault rifle.

First produced in Russia in 1947, the Kalashnikov was and remains one of the most effective killing machines humankind has known. During the Cold War, it was Russia’s vast nuclear arsenal that kept minds focused in the West, but it was the lo-tech AK-47, made in Bulgaria and a string of factories throughout Soviet Europe, that fuelled the hot proxy wars that raged across Africa, Asia and Latin America. Today, an estimated 100 million are in circulation, equipping revolutionaries, civil war combatants, terrorists and gangsters alike. Cheap to make and near-impossible to break, its mechanism is so simple that a child could use it, and all too many have, from teen armies in Sierra Leone to Isil ‘Cubs’ in Mosul. According to some estimates, the gun kills up to 250,000 people per year.

After communism’s collapse, the factory at Kazanlak – which operates under the trade name Arsenal – nearly went bankrupt, shedding most of its workers and leaving the town of 50,000 all but destitute. As the Iron Curtain came down, the AK enjoyed what many Western experts thought was its last hoorah. Tens of thousands of surplus weapons held in old Soviet stocks were effectively looted by arms dealers and found their way into the hands of everyone from Rwandan militias to South African mercenaries and Colombian paramilitaries. Many of the missiles, rockets and Kalashnikovs flown round the world by Viktor Bout, the Russian arms dealer who inspired the film Lord of War, started their journey here in Bulgaria.

Almost 30 years on, the production lines in Kazanlak are once again up and running. Its fortunes have been revived by an uptick in global conflicts, and by Bulgaria’s decision to abandon its Moscow allies and join both Nato and the EU. In 2017, Bulgarian arms exports alone topped £1 billion, a level not seen since the fall of the Berlin Wall. All of a sudden, the AK business is booming again. But this time it is under EU control.

How, arms-control experts ask, has this been allowed to happen? And what, if anything, should we be doing to stop it? After all, the worry is no longer solely about such weapons falling into hands of child soldiers in the Third World. One of Arsenal’s lucrative new sidelines is a semi-automatic ‘hunting’ version of its Kalashnikov product, available in shops in Bulgaria and many other EU countries. In the light of the Christchurch massacre, which saw New Zealand ban such weapons, should the EU consider following suit?