Europe's biker gangs set on a collision course with the police

In the middle of May this year, thousands of leather-clad bikers from across the Balkans gathered in the Croatian town of Slavonski Brod for a bash celebrating the unbridled joy that comes from tearing up the open road on a powerful two-wheeled hog. The annual Moto Klub Brod motorijada (motor picnic) has become one of the largest gatherings for outlaw motorcycle gangs in the Balkans, taking place on the border of Bosnia-Herzegovina in a Croatian town that was significantly damaged during the war.

Despite the ongoing tensions in the Balkans – and the fact that many bikers are hardened veterans of the successive wars that tore this region apart in the 1990s – the Moto Klub Brod normally passes off without incident. But this year, on the last night of the seven-day festival, a large brawl broke out between a group of Hells Angels and a rival gang from Bosnia known as the "Grevinis".

The fight, which began when a group of bat-wielding Hells Angels attacked a car carrying Grevinis members – and ended in police having to stop an angry crowd from beating up the Hells Angels – had little reason to be reported outside of the local Croatian media. But in the offices of a number of police forces across Europe, the fight caused a buzz of activity and concern.

Those charged with investigating drug trafficking and cross-border gang crime in Europe have watched with trepidation as outlaw motorcycle gangs, dubbed OMCGs, have spread with renewed vigour across Europe, particularly in the Balkans and eastern Europe. Investigators say this increase is no coincidence. Both areas are vital drug-smuggling routes from Central Asia and South-east Asia, where almost all of Europe's heroin and much of its cannabis originate.

According to Europol, the EU-wide agency that collates criminal intelligence on cross-border gangs, Europe is now the continent with the highest increase in new OMCG chapters, many of whom are involved in extortion, racketeering, sex-trafficking and drug smuggling. During the past five years the Bandidos, Hells Angels and the Outlaws have opened more than 120 new chapters, bringing the total number of European chapters to at least 425. By comparison the number of chapters of the same trio of outlaw gangs in the United States and Canada is hovering around the 300 mark.

The threat posed by the expansion of "one percenters" – the term outlaws use to distinguish themselves from the old adage that 99 per cent of bikers are law-abiding – has concerned Europol to such an extent that this week they organised a conference in Dubrovnik gathering officers from across Europe to discuss how to investigate, target and disrupt criminal biker gangs.